Never made any custom content before? Start with the easiest, most basic stuff (which you can make with all free programs) - Sims 2: Walls, Floors, and Ground Cover, Sims 3: Custom Patterns
Just installed the Sims 3 patch or about to? Read this article for helpful advice about patching and keeping your custom content working!
Don't upload my lots or my neighbourhoods on any site !!! You are free to use them anywhere else !
If you use them for a visual creation, giving credit would be friendly.
If you use included custom content for an upload, please read it creator's policy.
Mine is : do what you want with free sites but giving credit is ever friendly !