How to play Twisted Fate?

I normally go AD TF, but I tried to play AP midlane TF just now, and I don't get it. I have good waveclear, and I still have good roam potential, but I'm just useless after laning phase ends. I know I can gold card priority targets, but other than that I don't get it. My damage sucks (probably because I rushed Zhonya) even with a full combo. I don't understand what to do, what's my purpose besides stunbot. Unless that is my only purpose. Can I get some advice from some TF players? I'd appreciate it.