The terror of the void was the first champion I played for more than 3 games. Once I picked him up I instantly fell in love and played no other champion for months. I played bruiser or tank focusing on physical damage for a while. I lost interest after a while and started to play some simple mid mages like annie and veigar. Then after getting a few wierd looks broke out good old Cho'Gath as an AP Carry. His spells scale well enough with AP to deal large amounts of burst damage. I went on a streak of no losses with him when I started doing this.

Carnivore is where most of your sustain comes from. Both the mana and health regain can make going after some minions viable where otherwise the harass would be too good for it to make any sense. Rupture can work as a decent initiator but I wouldn't rely on it too much. If you do hit it then be prepared to follow up though. It also works as a great combo starter with your other skills. With Flash if an enemy is fleeing you can catch up and plant a rupture to get kills you otherwise wouldn't be able to. Feral Scream is a good anti-caster damage dealer. Try and hit as many targets as possible with it. Rupture is great for giving you oppurtunities to use this. If you are having trouble landing it remember that the hitbox takes place at the beginning of the animation contrary to how it may look. Vorpal Spikes are great for minion killing. I get level 1 of this first as it helps you secure minions you otherwise wouldn't be ablt to but otherwise doesn't have much utility. They increase your damage a good amount and give it range. You can use the range to hit sorcerer minions without sacrificing your position, or to harass a poorly positioned enemy. Feast is what makes enemies fear being near you when below half health. At first it is mainly used just for getting the stacks up. Be weary of mana when you are building these. After you have all 6 stacks however it is a wonderful true damage nuke which scales with AP. If someone is low you can use this skill like an assassin and instagib someone from a bush.

Farming is a large part of any mid player's job. Farming is especially important for Cho'Gath as he is very item dependent and his passive gives him both mana and regular heal on kill. Cho'Gath's skills do a good job of farming during any point in the game. During the early game his Vorpal Spikes not only do a good job of killing minions at a higher health, but also can kill sorcerer minions from the front line without having to worry about getting too close to the enemy mid. As the game goes on for longer and you gain extra

Flash is one of the best escapes in the game. And it gets even better later on in the game as Cho'Gath's hit box starts getting obnoxiously large.
Exhaust is also a really good spell for Cho'Gath as it makes landing a Rupture plenty easier.
Ignite really helps with killing health regaining champions like Dr. Mundo. It also synergizes with your already large amount of true damage from Feast.
Teleport is a great spell for pushing lanes, reaching team fights, or saving turrets.
Cleanse acts very similar to Flash but helps break out of hard cc. With Cho'Gath's high health he doesn't usually need to get away immidiately anyway. Unfortunetly it doesn't give much offensive capabilities which is why I prefer flash.

kage's lucky pick

Sorcerer's Shoes help deal with magic resist before you can get out a Void Staff, but once you do it makes sense to replace them. Both Ionian Boots of Lucidity and Mercury's Treads are good choices. Kage's Lucky Pick is a good idea to get out early if you are building Deathfire Grasp (which we are) because of the gold passive and ability power. Rod of Ages is a good choice for Cho'Gath because his early game sustain is important but starts fading into the mid game. catalyst the protector helps with this and the scaling with time is great for a champion not meant to be an AP carry. Rabadon's Deathcap is such a good pure AP item that I had to put it in. And it becomes better and better the more AP you have. Deathfire Grasp has really good synergy with the rest of this build. The Void Staff negates 40 percent of magic resist and Deathfire Grasp does a percent of the opponents health as magic damage. The high amount of true damage Feast does forces an increase in health. And the void staff makes magic resist attempts null. Lich Bane Makes your combo deal so much more damage. 100% scale from ability power on a melee attack is so good on Cho'Gath.

Pros Lots of true damage Best skin(s) in the game Great CC Unexpected mid Great sustain

Cons Big hitbox Low range Reliant on Items and Feast stacks Team might think you're a troll