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!
I'm working on making a slimmer driveway, and I've been having one heck of a time with the scenegraph. Everything says its connected all nice and everything, but when I go to load it in game, the texture is funky when I pull it from the catalog and when i actually place it the texture/mesh disappear. The object is there because i can place a car on it, but it visually isn't there. What did I miss?