[YesEvil]

I got have plenty of ideas myself, but I would highly reccomend you try out the current blink obs build, here. With your 4 gate, I don't know exactly what you do, but a pylon to warp in on the high ground would work exceptionally well if you get vision, target sentries.

But as plenty have stated, in the end it comes down to your scouting. "Thus it is in war that the victorius strategist seeks battle only after it has been won." - Sun Tzu

Know what the enemy is doing, and deny him knowledge of what you are doing.