Structures

Command Center: This is your base of operations. It does cost more than a Zerg hatchery, but it has the special ability to lift off and fly. This makes expansions on island maps faster than the other two races. The command center also can support either a comstat add-on or a nuclear silo add-on.

Comstat: This is the best scouting tool that the Terrans's possess. It allows them a brief view of the screen at some point on the map. It does run on energy, and shouldn't be wasted, nor be saved. You should always hot key these buildings to allow for quick usage if needed. They are detectors and can reveal any cloaked units while the comstat effect lasts. It doesn't hurt to have a lot of these, because at the end of the game, it becomes possible to see the whole map.

Nuclear Silo: These add-ons are mostly used for fun. They do produce the best weapon in the game, yet it takes a long time to gather the pieces needed for a good nuclear strike. Unless you like long games, you shouldn't bother building these. They don't provide the offense or defense of battle cruiser, and use up a lot supply depot while you stock up on them. They are very effective if you can mass produce nukes, meaning making several silos, prefferably 5-7. I used to do nuclear rushes back in 1.03, of course it was for fun, but it was very effective. With the new decreased build time of a nuke, you would be able to nuke almost non-stop, causing serious damage. This also can be accomplished on only 2 bases, yet you would have to sacrifice a lot of advanced units, as tanks, wraiths, science vessels.

Supply Depot: These don't do anything useful, except take up space. You can form very good barricades with these structures, making it very hard to break a choke point. You should always build these in advance, so you won't get stuck at your production limit.

Refinery: The Terran's have the ability to build an unfinshed structure. This is useful, if you want to prevent an opponent from acquiring gas early in the game, by building a refinery on top of your enemy's gas site. You should then cancel it, by clicking on your scv, and make the scv run away. You'll have an unfinished building, yet you also have a good early spy, that can keep an eye on an enemies base, till they get military units. You should cancel this structure as soon as they start to attack it, which will refund the money you spent to create it.

Barracks: This is the first offensive threat that you can produce. It also leads to the production of bunkers. Barracks make good barricades as well, having the added ability of lifting off, acting like a door. They make good structures on island maps, since they do produce range units, which can protect you island expansions. They can lift off, so building or floating barracks to a crucial point is helpful, especially since the distance of walking to that point is very long. This is a good startegy, since most ladder maps have long paths making it hard to create a good land attack, so shortening the distance travelled is good.

Bunker: These are very strong defensive structures, especially with a group of scvs around. They'll increase the range of a marine. However you shouldn't build too many of these structures, since they usually are a waste of money. They're the start of a good containment though, especially early in the game where there are a shortage of siege units. Basically try to use these for offense rather than defense, since early in the game requires a good management of resources, and building a bunker slows down production.

Academy: This is necessary, if you plan to use marines. The range upgrade can be researched here, making marines very good once they're set up defensively. Also stim pack is the best weapon against the Zerg. It'll make your marines better than there hydralisks, since it'll double the damage they'll do. It also isn't bad for defense now, since you can get medics, which will be useful for making those marines last.

Engineering Bay: This structure is now a necessity, since many people will start to use lurkers and dark templars. So altering your old build orders, will be troublesome, but it's better than dying. It's very unfair to the terrans now, since they'll have to spend resources on missile turrets.

Missile Turret: These will built all over now, since terrans need the early detectors, since a comstat isn't enough. They're also necessary now on a tank push, adding making it slightly harder to perform but it also helps as well.

Factory: You should build the machine shop right away after this is completed, since it'll give you access to siege tanks and spider mines. You should almost always build two of these, since it's possible to support two factories at once with a starting base. Quick production of tanks will give you the upper hand, putting your opponent on the defense, since they're is nothing stronger than them at this point.

Armory: This leads to the goliath with is probably the best island unit. It also can upgrade 4 different aspects, making it good to have more than one of these.

Starport: The starport is cheaper now, as with the control tower. This makes it slightly easier to produce wraiths and air units. I don't usually build too many of these, unless it's time for battle cruiser production, since wraiths do suck, science vessels snd dropships are expensive, and Valkyries aren't all that great without other units.

Science Facility: This is the final structure, allowing marines to upgrade to 3/3. Of course it allows for the production of science vessels, which are very useful for irradiate. It also allows for the construction of battle cruisers.