Basicly, a 4x4 cube that can be spawned via a vehicle spawn that can be pushed however cannot be driven/rode/etc, and can be colored the same color as the vehicle spawn.
I need it for a boss battle where chunks of the building you're in are falling left and right and you can pick them up with the gravity gun and launch them at the boss.
I can also see more useful aspects for this (pushable crate puzzles, 'catapult' weights, 'bomb' projectile, etc) so it would be pretty revolutionary or something like that for more complex builds.