This is a classic Terran opening. A calculated risk because this Build Order will be effective against Nexus-14 or 1-Gate-Expand openings. Speaking of risk, being able to reed the game and good micro management are necessary. You will need the best positioning for your Buildings while keeping your main goal in mind: having an economic advantage!
Supply Depot
Command Centre
Barracks
Barracks
Marine
Orbital Command
Orbital Command
** the numbers 10/12/15... refer to your population in the game **
*** Also don't stop your production of SCVs! ***
Generally you can use this Build Order when you play a match or tournament which is played in several rounds, otherwise this strategy will be limited. Also you need to position your buildings so that they can help you if a Protoss decides to do a timing push (place your Supply Depots in front of your Bunkers for example). This strategy is seldom used when you play a BO1 (best of 1) because there are no surprises for your opponent in early game, since in most cases it will be possible for your opponent to scout your base.
However, different strategies are available to you when you created your new base:
• Start with a standard BioBall (3 Barracks with MMM) and start a timing push at 10 minutes.
• Take your two gas directly after starting your Orbital Command on your Command Centers and start a timing push using Marines and Siege Tanks.
• Take a new base (B3) if you have scouted that your opponent had started a Nexus-14 or a 1-Gate-Expand.
• Simply add Barracks and go all-in based on a compositions of Marines and SCVs.
