More Walls (100, not 50)
ALL the vehicals avaliable in the game(Like how reach has Forklifty and troop carrier in campaign but not forge)
Better Decorative Pieces
Ability to change wall/block colors(Ex. Tan, silver,Black etc.)
Maybe a digging tool?
They also need to do a way to set up custom firefight maps.
They could do drop pod zones and drop ship zones in spawning. And also span zones for Covenant.
What all do you guys want to see in halo 4 forge?