That contest sound interesting, I've even made that kind of thing back in the past. I'll maybe do something for you. About the schematic size, my heaviest building which is about 100*40*50 only weigh 42ko, it could help you.
However, I've got few questions about the project:
-Is it necessary to have an outside (decoration for example)? I mean, if I do something with everything needed in a close area, inside a building, is it alright?
-My project size will be 70*70*20 : any objection? (you have no choice indeed haha^^)