I've been using Ezreal for half a year in Dominion and Summoner's Rift.
Ezreal Build Guide :: League of Legends Strategy Builds
That's my AP Ezreal guide, extremely detailed and mainly for Dominion.
For Summoner's Rift, I use a similar build. I believe cooldown reduction is vital on AP Ezreal - watching when to nuke with your Arcane Shift and Essence Flux is also a necessary skill, plus, I've pulled off epic blindshot ults.
I'm also very skilled in last hitting - that is something you'll need if you want to play AP Ezreal. I prefer AP Ezreal over AD mainly because I can't get the feel of auto attacking and like to burst down people.
Furthermore, he's much more stronger late game, and his ult can hit for over 1k, as of three of his skills also scale off AP.
Up to you, really. I did very well with Ezreal when I played him AP in ranked, but when I started going AD...I kind of failed. xD