never use a pylon for part of your wall if you are going FFE
Also in that build you put down a forge then the nexus before gateway and cannon. also when going dts get a warp prism to warp in zealots with. Generally people wont notice the dts until its too late.
Scouting, send your first zealot to see what your opponent is doing. If you sense roach all in, make 3 more cannons to defend.