I know that I am not the only one who enjoys creating thier own Sims, Sim households and building thier homes. Even if you do not use CAS or build homes I believe as a player you have or can dream up some interesting possibilities! Singles, couples, big family, small family a multi generations household? Basically thier ages, gender, genetics, personality, turn on and offs (the basics). Personal Bios or back story. What type of home do you envision for them? My new custom town needs Sims and Families and I need your help! (Please and Thank You)

You could roll dice to help you decide? That's what I do when I find myself playing the same 'type' of sim families again and again. And use a random number generator to decide how rich each family is when you build their home, so you have a good variety from trailers to mansions.

When I created CAS families, I almost always create families with single parents or families with adult siblings. Or I make a number of diverse YAs, including some sibling pairs.

Sure, make a couple of nuclear families, but not everyone.

Pick one person and build a family around them:
- a matriarch with two sons, both married, and grandkids
- a toddler daughter whose parents are divorced
- an adult who lives with her best friend and her best friend's teen sister (make as adult in CAS)

Genetically, I try to heavy load it with blond and red heads as brown & black will dominate but it's so fun when a recessive Gene pops out. Also I lean into the darker skin tones as I also find that since 1 & 2 are only a little different, you just have more of those than 3 & 4. But maybe that's also because so few of the pre-mades are diverse.

I think Pickles89's ideas of rolling could be great, especially for deciding wealth/property.

Depends on what you want to do, really.

When I started a BACC, I rolled for number of Sims and Gender. I ended up with four males and one female. I then decided that the backstory would be a pair of siblings inheriting a farm from a distant relative, and a group of friends from college decided to go with them.
Aspiration and life state was also rolled, and I tried to diversify them. One was a plant sim and the rest ordinary Sims. Then I played them for a week in the big farmhouse together, to see relationship and chemistry. None of them were attracted to each other, the plant sim get fighting with one of the other guys, and the rest were good friends. I had them marry random townie spouses and had them move out into small starter farms. The siblings and their spouses stayed, as the big farm really had space and needed the labour.

If I just want to add a family, I often do a challenge round (Asylum, seven toddlers or Orphanage, bachelor/bachelorette). For the BACC for example, I added a vampire who would have a baby and kill the father once every generation (kinda extended black widow challenge).

If I were to start a new hood prosperity style, I'll use this randomizer as a start to add challenge and a dice like Pickles89 said.
I usually use Nepheris' way here when I start a hood because I like to see how things evolve in game.
I often add single adult sims when it's needed but the latest addition was an elder woman to run the guest house.

For home, everyone starts out with a tent and live off the land. :D

I usually start out with six or seven families. In Poverty Point, they were based on the bin Sims, except that the Goodies and Newsons were combined into the Oates family, and I just accepted whichever gender of teen/child/toddler CAS happened to offer first (e.g., the Haywoods, though based on the Gavigans, had Jennifer rather than Isaiah). Otherwise, I roll a D6 to determine how many people will be in each family. The first Sim is always an adult, and thereafter, I roll a D10 for each family member to decide age and gender: odd for male, even for female; 1-2 toddler, 3-4 child, etc. Everyone is related in some way to the first Sim. Thankfully, I have never yet rolled for a single parent with toddler quintuplets, though it could happen!

As for housing, I have a rooming house with shared kitchen and bathroom, where a single 3x2 room costs about $60 and the largest two-room suite costs about $480, and a custom apartment building that contains four bachelor pads on the ground floor and two one-bedrooms upstairs, all priced between $450 and $860 a week. In some hoods, the rooming house becomes a barracks, with the bedrooms and a library on the upper floor and a gym, music room, dining room and pool hall on the ground floor; in that case, it's for singles in the military and room size is based on rank, not wealth. I use some of the Maxis apartments, too, especially the City Center Apartments, Tech Center Flats and Crossroads Apartments. I have a one-bedroom custom house and a cheap but spacious four-bedroom based on the Maxis 'Bonny Bungalow'. For two bedrooms, I mainly use the Maxis 'Just Right' and 'Tiny House' bungalows. Sims needing three bedrooms tend to either rent a townhome or buy the cheap four-bedroom. I use the 'Grand Estate' for the wealthiest Sim in the hood - it's actually pretty cheap, at only $65,000, but with high-end finishes it can be made to look expensive and it's a lot more playable than the other big Maxis houses.

I started my BACC out with an open air farmer's market on my community service center in Dodge and a homestead lot of the largest size with a few basic essentials for the first couple to settle into Dodge in the spring of 1840.ANother couple arrived the following spring and there's likely another coming in the spring of 1842 to start their own homestead and the two couples already living there also got workshop studios built and are using them as temporary houses until they get their family homes built.The third couple will do the same as the others and they'll have to get it built before their first winter.I also buily my own homes,apartments,community lots,hotels,dorms and campgrounds as I add the new districts though my first is to be a shopping district to move the farming out of the town center as the population grows and I'll start adding families or singles as the town grows and kids begin growing up to provide the kids growing up with possible marriage partmenrs they might befiend as children.

I usually start my hood with 4 founding families. This particular time I had two traditional family units, M/F, and one gay couple, M/M. The last household was a single male romance sim. I made all my townies. I do them in batches of 8 and start off with 16 townies and 16 downtownies all adults. When I add Uni I make the dormies and start with 24 or 4 batches of 8. When I add vacation subhoods I also make the locals and tourists, as a base I go 8 locals for each destination and 4 tourist families. This is my bare minimum starting hood. I randomize every single one of them as far as personality, gender preference extra. I use the Simblender to do it or I roll the dice and in the case of a 50/50 I flip a coin. In the case of the playable families, I do make them compatible in the case of the townies it's just totally random.

I build from here by having families or singles move to town as I need to add more sims. I add townies as teens usually and then age them to dormies within the same generation. When dormies have hung around for a while without hooking up with a playable I age them up and make them townies. So my hood population grows slowly but it does grow. My founding families are not allowed to intermarry so they are going to be drawing from that pool of townies I've created. As I pull more townies into the playable population I create more to take their place again usually adding them in as teenagers.

As for houses, I play an empty Pleasantview and I will end up bulldozing the majority of the houses and rebuilding. I do this as needed though so I don't end up having to build a whole town before I can even play. There are a few of the houses that I just make changes to and use. For housing ideas, I like to look at what people are building and putting up to download. I build my own but I certainly get inspiration from others.

As you can see we all do something a bit different from each other. It's what works for you. There are people who love to download lots from other creators and there are some amazing ones out there. You can also download pre-made sims if you don't want to make your own. I am personally a massive control freak so building a town from the base up is right up my alley. I'm a mediocre builder at best but I still build my own lots and homes cause that's what I like. I make backstories for my sims but they mostly are just basic outlines that I fill in once I get to know the sim. I used to keep spreadsheets and have a whole bunch of rules. I don't do that anymore I have a few basic rules and just let stuff happen. It makes it more of a game and less of a job, for me.

Thank you each and all for your creative, inspiring replies.

I personally play a medieval/history inspired hood. I don't know how much that helps you but I like to include different cultures and practices that I read about. For example, I have a traditional European inspired kingdom with a king at the top but I also have a subhood with a Ottoman inspired Sultanate that plays completely different. Then of course I also play a class system. It is easy to fall but hard to climb. There is also a chance of death in childbirth in my game which leads to quite some remarriages and early deaths. The men will soon find themselves in a war and who knows who will survive. I like to use random.org for that and it mixes up a lot of my plans but that makes it interesting.
For a modern hood, I would maybe consider adding different types of relationships. It doesn't always have to be just two people. Affairs and mistresses/lovers are also always interesting to me. I personally like to have every Sim to have a child eventually because my goal is it to open one sim's family tree and being able to click through the entire neighboorhood.
I'm trying to experiment more with the aspirations. Yeah the majority is still family but the romance, knowledge and money population is growing too. I just don't like pleasure and fame (sorry if the terms are not 100% correct, I play in German)

I think we could do worse than take our inspiration from Maxis. The base game families are most certainly not all the same. Look at Veronaville, the base game 'hood I know best. At Capp Manor there is an elder male and three teens -- his grandchildren. There are no adults. At the Monty Ranch there are two elders and two teens - their grandchildren. Again, no adults. But the Summerdreams, one may say, Mum, Dad and two kids -- they're a normal family! Except they're not married, and the kids are adopted. Oh, and they're all fairies!
What about the Veronaville bin families? Bianca - single adult starting out in life. Antonio - recently widowed young dad with two little children. Regan, Cornwall and Kent? Young married couple with the wife's brother living in -- and her husband hates him. That only leaves Goneril and Albany and their family. Well, if Albany, Goneril and their brood are a "normal" family, then all I can say is H**v*n protect us from normality!

The same is true of Pleasantview and Strangetown. In fact I think the Burbs are the only really conventional family in the whole of base game. So if all the families in your game consist of married couples with 2.4 children (or married couples with 14.8 children thanks to the Triplets and Quads mod?) then you really can't blame Maxis. In most of my 'hoods I aim to have a similar wide mix of household types, from elderly spinster sisters sharing a cottage together, to teens trying to enjoy their young lives without the encumbrance of adult supervision.

Variety, they say, is the spice of life!