hecarim has great ganks after level 3, after he gets his e.
this is my preference all builds can have slight variations if you really nitpick.
runes: attack damage, armor, mr/lvl, move speed
masteries: 9/12/9, armor pen in offense, hp and bladed armor in defense, rune duration in utility
assuming you know when to start boots or cloth armor
build: boots, wriggles, hog (if fed, ie wriggles boots and hog within 15min), trinity force, maw of malmortious, frozen heart, randuin's (if hog) or Force of Nature, sell wriggles for Bloodthirster/Black Cleaver is they are getting armor
my normal path is: boots, wriggles, hog, glacial shroud, phage, hexdrinker. From there its what I need more, if super fed skip hexdrinker and get triforce first, get trifroce before glacial shroud if you have enough to buy it up front