With terran there is a tricky, usefull thing you can do with the buildings, or at least a few of them. Well you do this by finding your opponents base. And after you find that base, you build an outpost/ little base next to it. Get two barracks right next to his base, and when you have a good amount of minerals, send in scouts to see if you can slip in un seen, then lift them off, and fly into his base out of sight, and start building men, send 10 or so guys to attack the front to make him/her send there men to front to kill you. And you will be building guys in his base. After you get a good little force attack, but keep building guys there. If you win good, if you dont win send more guys from your barracks. Remember this wont work to good if he sees you, try to find a corner or somthing that is not being used.

CreepColony's Opinion: If you can slip an SCV into their base and build the barracks from inside, you can have that SCV later build bunkers and repair them, which will be really devestating.