I was busy cleaning a pot with World of Goo music playing then I realised a fun gamemode would be a Tower Building one. Not a building competition or anything like that, a tower gamemode where you get limited or unlimited bricks but bricks have "Weight", bricks can only hold so much "weight" before destroying themselves under the weight of all the other bricks. This would force players to build more support for there towers, the bricks could be color coded for there weight stress load, like Green = No problems, Yellow = On its load, Red = Going to break in the next 10-20 seconds (This allows players to build support before it'd break). This could also be used to build bridges/structures challenges with brick load limits.