Introduction
This is not a tank build. This is a mage build, and as such, Cho should be played like one... ish. I've spent a long time trying to understand how to play cho a successful mage, and I've failed build after build. Though I'm confident after several hundred games of playing this guy that I've found a really good mix if played well. Also, It's all about the rupture! If you can't land that, than your not going to do well. I would say this is true even if you level up the scream first.
Masteries
9-0-21. I mainly appreciate the 9 offense for the cooldown but obviously the extra ability power and magic pen work well too.
the 21 is especially good for the movement speed as cho needs to be quick to escape ganks and get into the enemy's face in order for him to feast. The experience helps a lot in out leveling the other champion and just about everyone else. The more levels you can get ahead of the other team the more you might have to fight that whole god complex thing.
Items
Starting with a Regrowth Pendant on cho is almost seemingly a d*ck move to do. With cho's passive carnivore, coupled with this, Cho just has so much more sustain.
Philosopher's Stone: Pretty good for cho, usually helps his mana problems early game, though I try not to use much mana until I reach level 5 or 6.
Sorcerer's boots: When Cho gets these all of a sudden you should notice a fairly good difference in how hard cho hits. To me, it's like night and day, so if your doing it right the other guy should be more cautious if they weren't already.
Rod of Ages: This makes a cho with 6 stakes even better. Though I make sure to buy the blasting wand first as the extra damage really works.
Nashor's Tooth: Probably my favorite Item on cho. This also may seem to be a wtf kind of item but this is where cho's auto attack's mean something. Vorpal spikes will actually benefit you, plus the 25% cooldown brings your cooldown to 35%. This item has saved me so many times when my abilities are on cooldown.
Rabadon's Deathcap: Ya.... It's a lot of ap
That is my main part of the build. The next is to see what the enemy is building. sometimes I'll build a void staff if the other team has a lot of magic resist. Though if they are not, I'll go with this sequence.
Abyssal Scepter: The enemy team doesn't have a great deal of magic resist and an extra 20 to give you 40 magic pen works out well. plus having magic resist is always needed.
Randuin's Omen: By this time you should have enough health where if you do get in the middle with everyone else, pop the active on this and go all out. The nashor's synergizes well to put out damage when your cooldowns are up, while this keeps you alive long enough to make something of it. plus, with the item and masteries, the extra 5% cooldown as laughable as it is actually brings you to a perfect 40% cooldown.
Summoner Spells
Ignite and 
Flash. It's pretty hard not having flash to get out of bad situations, and Ignite can dot that much more damage to either save you or to just kill the other guy. fun to use against mundo's top lane that don't understand why they just died..... and than come back and do it again. Anyone else see that with mundo? .... ya.
Pros / Cons
Pros:
very scary in lane
does a lot of damage
can normally three combo carries or just squishies.
cons:
Not a tank
Can't initiate
kind of have to land ruptures....
Unique Skills
In this build Cho' Gath just starts off weak. so last hitting is probably more important than normal. If last hitting isn't possible through melee because the opponent's harass is hitting to hard, than try to last hit by placing ruptures. keeping Cho'gath healthy until he reaches level 6 is more important than keeping a full mana reserve. plus, around level 6 I will normally have sorcerer's boots by than, and with the runes catching up a little his rupture starts to hurt. so, now that rupture's hurt, how to land them. In truth, they are hard to land and if you cannot, your team mates and yourself are the ones who will suffer.
landing rupture[/b]
1. A good way to land rupture is by placing it by a minion the opponent will most likely try to farm. This can be trickier with ranged opponents but if your hiding in a bush and they don't know, this can be a more sure fire way of landing the rupture.
2. If you or a teamate is running away with very little health with the opponent chasing, always place your rupture toward the fleeing victim. This may sound dumb, but a lot of times I'll have to force myself to go back to this rule, because the opponent may have very little health as well. Logically, I think that the person wouldn't just sacrifice themselves to go for the fleeing ally, so when I place rupture towards the opponents escape route they normally don't take it and kill my ally. I see people dive turrets when I am clearly going to rupture them. I don't get it, but using this method, the worst thing that's going to happen is you'll have saved your ally, and the opponent will get away. with such a long cooldown on rupture, you should always take the route that would potentially save an ally even if you think placing it would lead to nothing. a lot of times you would be surprised. and I'll try to post a video about what I'm attempting to talk about here.
3. using rupture in a bush works wonders, even if they know you just went into the bush. To hide the wind up and stomp prevents the opponent half a second less time to prepare for the rupture.
Build Guide
Discussion (9)
Greater Mark of Hybrid Penetration, because once the 
Greater Seal of Scaling Ability Power, because I want ability power stacking with levels. It just causes him to hurt a little bit more.
Greater Glyph of Scaling Magic Resist, because magic resist is important on Cho as he does not stack magic resist as he levels.
Greater Quintessence of Movement Speed, because as a mage, cho cannot always be in the thick of it. but he does need to move in quick when possible. This is also great for early game as it's hard to catch a cho that doesn't even have boots with these quints and masteries.
