I go 21/9/0 masteries with sorcery (cdr) mastery. My build is, rush Tri Force, then BORK, then IE, then Last Whisper, and then Mercurial Scimitar (or other defense item) My boots are sorc shoes. I'm new with Corki, so how good is this build?
Corki was the first ADC I picked up, and while I don't ADC often, I do well with corki. That being said, I would say your build is decent, but avoid rushing triforce. I prefer to start with a bf sword into bloodthirster, then triforce. Triforce is obviously a must, but because its so expensive, you lose early game pressure by trying to focus on it too hard. Besides, its not good until you're level 6, and a bloodthirster can be completed faster than that. I also feel that rushing ad quickly is a good option for him because your auto attacks deal true damage based off of your ad, and your q gets really beefy and turns into a great kill secure before level 6.
Next get boots and triforce, then build situationally. I don't think sorc shoes are that important for him because the true damage is what you're after. I get Ionian boots or greaves. Bork and IE are great choices. Only get mercurial if you feel you need the mr. You should he well out of mid lane's range during teamfights thanks to your ultimate.
