hmmm

imo, you shouldnt use heal, use flash instead. frankly i would get boots of mobility, a black cleaver and 4 bloodthirsters. twitch doesnt really need attack speed with his ult and ambush. And madmack is right about your masteries, i recommend 21-9-0, or 21-0-9, because twitch is a little mana hungry.

You need to check your masteries as well. They're a little messed up.

Okay, i see where you wanna go with this build. You simply want a bunch of Attack Speed But, Attack speed without more than a Black Cleaver wont work, you should get rid of a Phantom Dancer and Last Whisper, and Get a Bloodthirster and an Infinity Edge.
and then you should add a little more Description, but im not going to downvote, since i think you should have the chance, to make more Info. And come with your opinion.

for you to get the most benifit out of black cleaver you will have to hit your target at least 5 times, i find that with twitch if there not dead in 5 attacks (or at least severly injured) then they get away, its a great build for poppin your ult and mowing down teams but i think there are better items for that than black cleaver

Pointless, better is 3x blood thirst 2x phantom dancer and 1x Infinity Edge. With that things you can simply 3-4 shot squishy targets (example: Sivir is going down after 3 criticals and 1x normal shot (when you have 2,5 attack speed with both buffs from stealth and ultimate sivir will be dead after 2 seconds. She didnt even notice that). Sorry for my english but im still lerning.