Ah I understand. How about something a little bit more basic, but still good. In the map editor, you could make it possible to build a stand alone 'wall' for a house, and allow the designer to choose the size of these walls. In this way a map designer could connect the walls together themselves and have atleast a little bit more variation with the buildings.
However I realise this brings up possible problems with having the building properly textured. I suppose this could only be fixed by having the map designer fit the texture after the building has been made.