Against Terran:
  • Don't scout with probe
  • First pylon in main minerals so 2 cannons can stop fast reapers (2 perfectly placed cannons can cover nexus, forge, and all probes from reapers).
  • Pylon at expansion choke (or near expansion if map has no choke)
  • 1 cannon at expansion
  • Nexus
  • 2 cannons at main
  • 1st gateway
  • If reapers have hit, build 4 gas, if they have not hit 2 more cannons at expo & only 2 gas
  • cy core, scouting with zealots
  • robo and starport
I rarely build more than 1 gateway until late game (1 gatway with double chrono will keep money spent well enough, especially with forge upgrades). When the starport is up I generally make void rays non-stop the entire game (with chrono boost). PvT usually evolves to a macro game with immortal/stalker/void in varying combinations depending on what they have (gas intensive, yes, but with dominating immortals @ ~5 minutes in extra minerals can be used on fast cannons/expos. Have to force self to expand & cannon, not dump minerals on useless zealots in late game).

Source : Starcraft 2 Armory - Forums : Always fast expand verse terran?