I still say that if nothing else, at least check out this guide.
Also, why Warmogs on Cho'Gath? He already has an HP steroid, and further HP stacking just encourages people to get Madred's. Besides, you need some CDR to help spam your abilities. Warmogs is only viable when you know the game is going on for a long enough time for you to itemize the rest of your stuff, like CDR and Auras.
Honestly, Cho'Gath can build anything first. RoA, Rylai's, Frozen Heart, Aegis, Sunfire Cape, Banshee's Veil, depending on the enemy team.