This can only be done on a mucho$$$ map (you can do it on no muccho maps as well if you have a lot of minerals).

If you get tired of building those stupid supply depots which cost a lot of space, and you got some minerals, start building command centers. They provide you 10 supply (even more than a depot) and you can lift them so they won't cost any space at all. Watch out for scouts!!!

CreepColony's Opinion: Ummm...command centers cost 4 times as much money and take much longer to build. Only do this if you got rushed early in the game, built your base in your allies base, and have limited room.