@wrathdylan
As Tessasia33 said above, derivation can be a faster job, and at the same time swap textures, opacity maps and blablabla. Now, you mentioned 'creating', if that's what you're thinking, rather than 'deriving' from some other creator. you will have to use Blender or 3dMax, or another similar, sketchup, Revit. After that, export the fbx at the correct scale so that imvu doesn't show errors, and of course, add points so that players can walk around the area.
It can be a little more complicated if you're a beginner, my advice? Go to the store, find something beautiful and open your living room, in the beginning that's what I did and over time learn how to work in rooms, furniture, avatars. It's a lengthy process, you don't learn overnight, but once you learn it's fruitful.