This build gives you the really nice burst damage you are looking but it will keep you alive as well!

Quintessences: i take spellwamp be cause it is gonna keep you in mid lane, and you are are not gonna need the will of the ancients, be cause of your passive, and the masteries and the runes.

Mark: i take magic penetration to give you an extra burst vs tanks, and now void staff is not needed!.

Seal: its mostly just to give you some damage early game.

Glyph: you are gonna have some mana problems early game, and that is why you need those runes, to constantly harass the opponent without worrying about your mana is low.

Offense Three: i take down to the magic penetration so i can get a nice burst vs tanks, and i get some cool down reduction too which is vital for this champion.

Defense Three: nothing

Utility three: i take in the utility three to get the gold, and the spellwamp, and the cool down reduction, and the mana regen and all those are vital to you trust me, and the gold increase do so you can buy a health potion at the start of the game, and thats really nice to have.

Orb of deception: truly your key damage spell take it first, if you know how to hit with skill shots if not take fox fire first.

Fox fire: and this is the second one you take if you can hit with skill shots, its easy to hit with just be near them.

Charm: it don´t do so much damage but its really nice to have when you are in trouble, or you can use when your enemy is in turret range, and then you make them walk closer, always funny.

Flash: pretty much standard mage spell.

ignite: again pretty standard.