root/map_source/prefabs/(you can add folders in her if you like if not just keep it in prefabs)

This is a prefab that i made in a few minutes so that people could see how it could be formated. This is of two telephone phones connected together, all the textures are defaultly in radient.

Right click in the 2d view and hover over misc and click prefab then navagate to wher you put this prefab(or any other)