What I gather from all this, and please confirm if possible TotalyMoo, is that those buildings were custom made in a 3D app, imported, and then the trees have been added to the lot.

But I wonder if textures are generic repeating textures from the library of existing textures in the game which have been applied to a UV mapped imported building, or if the textures need to be part of the package prior to import. I fear tons of user created mods will chug a lot of space (and VRAM) over time, vs. using existing assets.