Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
The build is pretty similar to many of you standard builds, focusing on AP, pretty standard.
But the main difference in this build is Tiamat and the Hextech Gunblade.
Pointless items? Maybe, but tiamat adds a splash area to your basic attacks, this combined with your passive, and ranged distance allows for effective farming, allowing you to gain the items you need.
the Gunblade works with this, improving both AP and AD, the spell vamp is also extremely useful.
For those that are un-convinced by tiamat and hextech, you can use the Crystal Septer, and Will of Ancients. This ups you spell power, adds slow to your spells, and still gives you the spell vamp.