So, I downloaded the Dereliction House, which is an amazing thing(http://modthesims.info/d/264529/dereliction-house.html) but in my game, I want my simmies to slowly fix it up, starting with the outside.

Unfortunately, there's a few sloped tiles, on the front and the back.

I found this thread, but it looks like the images got eated. http://modthesims.info/t/246349

Anyone have an easy way for me to get rid of these? Use of CEF is so hairy and it escapes my building abilities.

You will have to use the CFE cheat to fix the sloped floors.
Once the cheat is running, there are two main methods to flatten warped floors.
1. You can drag the floor leveling tool from a flat floor (on the same level) across the sloped area. If you just have a small area to fix, start from the closest point you can.
2. You can place a normal floor tile (carpet or whatever) on a nearby flat tile. The new piece of carpet will flatten the tiles around it.

You may also need to flatten floors on upper levels, if they have been affected. Then turn off the cheat.
It's not difficult, really, but takes some practice to get precision. Hope it works out for you! Sorry I can't get pics for you at the moment.

I am an idiot and I will own up to my shame.

I had typed boolprop testingcheatsenabled true, then boolprop constrainfloorelevation true, like an idiot.

No wonder it didn't work. I spent almost 90 minutes fighting with the floor tiles because the cheat was off...

Both of your options worked beautifully to clean up the couple of tiles. Now for my simmies to get to work.

It is a lot easier to put the cheat in and to be correct as to which if you put an Alias for this cheat into a userStartup.cheat file, just saying. I can share mine if you want to look at it.

Thank you very much but I almost never use it. Most of my build cheats are constrained to move objects and snapobjecttogrid. I'm a lazy simmer.

Glad you got it sorted.