Not Updated For Current Season
First item to buy is great if you start with a Vampiric Scepter after that get your boots and Haunting Guise then you have 50 magic penetration that do all your magic attack goes strait thru your enemies if they dont have any magic resistent...
Then start build your Hextech Gunblade and GuinsooÂ´s Rageblade then it is up to you if you go for NashorÂ´s Tooth or Malady... If you deside to not buy Malady another item who would be good is RylaiÂ´s Crystal Scepter wich give you some hp and more AP...
I am using this build for KogÂ´Maw and think it is really good enemies is going down really fast...