Decent build but i would like to see more of a description as why you chose certain items. Sun fire cape is unnecessary as an item and should be substituted by anything else and finish your rune build please. Also include some AP, cho' gath has AP ratios that are as good as any other mages. Finally s=you should also talk about his skills and his passive especially his ultimate seeing as how it can give him 900 health at 6 stacks

Nice build :)