Do a Left 4 Dead city with random AIs in almost every corner. Create like 10-20 warehouses full of weapons, and some could have secret basements or something, and buildings with really sweet details inside, like some kind of computer or something. Then create torn down buildings and very many sniping areas. Like a TDM, but 1 team destroys team 2 and AI and team 2 tries to get to the safehouse. Make really awesome buildings most builders wouldn't make: Power plants, military bases, offices, skyscrapers, woods, HQ, Theater, some other stuff. It would be awesome! (PM me when you're done, I'll have my BLID and full version by then)

P.S. make really cool weapons and changeable datablocks, and maybe some team-changers or decal-face-changers (If you can do that) Thx!