What are your AP Chogath builds?
When I started playing AP chogath, all I knew was that I wanted to be him. I asked for no advice on the subject and just made a build myself. My build basically focused on any AP item that had health as well.
It goes as follows:
Rod of Ages
Lich Bane (The little MR helps, but mostly for AP and Movespeed and the passive)
Zhonya/Trinity Force (Dont laugh at trinity force >< it works well for ap chogath imo because he is very much a hybrid type character)
Rylais is surprisingly good on him. With Rupture, it applies the slow immediately after you cast it. So it slows them down, reducing their chance of getting away. I personally didn't think it would work like that.