I researched that actually and not for SL but wanted to export Sims houses as models to look at them. In case any other curious person wondered same - you sure can look at them but the models are actually bonkers. In Sims 3 they are all stretched and skewed to the extent you have no idea what are you seeing. It is fairly odd as making mods to inject into the game is much easier than going about looking at construction geometry. So there is that, in case anyone wanted to know - I like looking into how all games' tick, pft.
However, in case of SL - you would literally be using assets you did not make nor have any creative rights to. Sure, if EA ever did sell them - they are free to do so ... but I assume even they would face some legal issues. Seems you are more after something to help you envision future house/decor so ... look for house decor programs or 3D software with assets built into it so you can easily make stairs, roofs and so on. Still, you probably would not be able to use them in SL but it could be a helpful visual tool.