For my summoner spells, I personally like to take exhaust and clarity. Cho'gath is a melee champion, but if played correctly, can be one of the most powerful in mid. The reason is he has great harassing ability. You can lock a target in place with rupture, but without exhaust, you cant really finish them off, before you really get too high level anyway, due to the short distance to their tower. This early game killing in imperative to your success. However, before you can kill them, you need to whittle their health down. The easiest way to do this is hit a few ruptures. However, this is very mana consuming, and cho doesn't have a huge mana pool. Clarity can solve that.

Like I said, rupture is going to be your main harassment technique. With your ability power, you should be able to take a large chunk of HP out with 1 hit, once its maxed. Getting it to rank 5 by level 9 in a key component to cho.

Cho doesn't have a lot of mana. That's why I start with the sapphire, so I can compensate for that. Also, rushing a rod of ages, which you should have by level 9, will cause rupture to do immense damage. Sorcerers shoes are an obvious choice. But, something you may be wondering about is the frozen heart. Well, cho gath is a natural tank. With a full build of this, you'll probably have around 4000 health, at level 18, with no feast stacks. Taking the armor from this is therefor, a good idea. Plus it supplies mana. But the real attraction lies in the cool down reduction. With it, you'll be able to throw out ruptures and feral screams very quickly. But, something else important is more feasts. These do obscene damage, and are imperative to use on minions to get the health stacks. Because of your natural tankyness, grabbing the rylis' is a great idea, as it grants AP and health. Warmog's, obvious tanking choice. The scepter gives you a great offensive and defensive versatility, as well as help any other AP on your team.