This Cho'Gath build has proven itself time and time again against human opponents. The armor and magic resist runes contribute to help Cho'Gath stay alive early game. The magic penetration runes allow Cho'Gath's feast and rupture abilities to literally take a larger bite out of the opponents. The swiftness quintessences are important mainly because no other quintessences really provide a significant enough bonus. Movement is ALWAYS important because it often is the difference between life and death.

I tried the pure tank Cho'Gath build before and discovered that while Cho'Gath simply won't die when confronted by between 1 and 3 enemies, it got to a point where the players would simply ignore me and go for the squishier players as my attacks weren't seen as much of a threat. This build gives us all the best parts of the tank build: Force of Nature, (Thornmail if enemy damage is primarily physical), Frozen Heart, and Mercury Treads while allowing Cho'Gath to bring out the oomph of his rupture, feral scream, and feast with Rod of Ages.

Probably the greatest thing I am currently up in the air about is the mana regen item: Philosopher's Stone. I know that there are better mana regen items out there but the extra gold generation in the early game and it's relatively low cost seems like a big win. I eventually upgrade it with Shurelya's Reverie for increased regen and cooldown reduction...but not until late game.

Unfortunately if you cut out any part of the tank set you lose a vital amount of magic/armor resist which otherwise Cho'Gath would be little more than a squishy meat shield. I do however stand by the Rod of Ages because they provide a significant boost along with a large amount of health and mana granted. Cho'Gath may not be able to take on 3 equal level players for very long without sustaining significant damage but having ability power and significant regen more than makes up for it because otherwise you are just a joke to the other team because you don't really pose a threat. All bark and no bite as they say. You have to know how to be aggressive without overstepping your bounds by yourself.

Just remember that different situations call for different pieces of armor sometimes. It is more important for Cho'Gath to have survivability BEFORE he has penetration power. If you are getting constantly ganked by heroes like Nocturne, Pantheon, or any purely physical characters (I don't know them all and it takes a lot of practice to find out), make adjustments to your defense accordingly and add more armor (say Thornmail and/or Frozen Heart) to make up for it.

One last thing to note: It is highly recommended that if you take top or bottom lanes that you have a ranged character with you. Since Cho'Gath is a melee character, he is prone during early game to be hit and run by other ranged characters. While the regen pendant and carnivore should make up for most of the health lost, it is better to keep the opponents at bay so you can get kills and get currency.

Do me a favor: try this build and please let me know what you think. I will always be watching my page and making updates accordingly in order to maximize effectiveness.

Pros

Great farmer
Can take quite a few hits
Good ability power- Powers hit VERY hard.
Good magic resist

Cons

Mana hog
Slightly squishier than pure tank Cho'Gath
Less DPS than pure AP Cho'Gath

The hardest part about using Cho'Gath is probably using his rupture in just the right place at just the right time. Sometimes you have to fake out your opponent and either place the rupture right in front or behind them significantly for it to land on them as they run away. this is easier to do when they are chasing you in a straight line or running away in a straight line as they often pay less attention to what is going on and more about getting away as fast as possible.

A successful rupture gives you about 1-2 seconds to close distance and immediately use feral scream to silence them and prevent them from really fighting back and possibly using exhaust if they still have a significant amount of health at that point. If you manage to get their health down to about 2/5 to possibly 1/3 then feast is more than likely going to kill them as it is true damage and bypasses magic resist. Unfortunately, feast has a long cool down and is best to have saved for heroes unless you need to make up some growth.

You are better off not wasting your rupture on minions unless you are farming a lane without an opposing player and there is no point to use feral scream on minions as it doesn't do nearly as much damage as rupture. Your vorpal spike passive ability was designed to dominate minions and it does get benefit from ability power. This is why I chose to have it upgraded earlier than feral scream because faster minion kills = more money. Feral scream is useful mostly for its silence effect.

After some consultation and practice runs i've changed my item lineup to better suit the build. First priority is the Philosopher Stone for mana regen/HP regen and that little bit of gold generation helps too. This allows you to use rupture more often and not have to get in close and potentially get ganked. Unfortunately Cho'Gath is really vulnerable early game. The boots of choice are generally the Mercury's Treads simply because of the magic resist and the decreased stun/snare duration. However, if the opponents in your game are primarily physical damage dealers then you will want to buy the Ninja Tabi for both armor and 12% dodge. At this point, based on what people have been complaining about in the comment section I decided to substitute Warmogg's Armor in next just to add an extra layer of padding and HP regen. It did turn out to be more effective, but costly. Now it is time to make your abilities pack more of a punch. Buying a blasting rod is a quick way to add more damage to your abilities and preps you for purchasing the Rod of Ages later on. The next set of armor to purchase depends again on what characters you are fighting. Predominantly physical: Frozen Heart first. This also adds a bit of cooldown reduction which, for Cho'Gath, is really nice. If they are playing hit and run, try Thornmail instead. Predominantly mage type damage: go with Force of Nature. The regen is very useful with as much HP as you should have by then. The next step is to finish the Rod of Ages and get a nice increase to ability power. I would say buy Rabadon's Deathcap as 200+ AP is a HUGE improvement but then you don't get the large amount of mana and HP that RoA gives. I may try this anyway and see how it works. Finally, purchase one last piece of armor, preferably the armor that you bypassed when picking earlier to make Cho'Gath a well rounded tank and damage dealer. Guardian Angel can be substituted if you like. If the game hasn't ended yet and you want more cooldown/HP regen/HP/mana regen then purchase Shurelya's Reverie.