This build allows you to outlast other players in lanes, your passive and potions allows you to stay for a very long time and that can make a huge difference in the early game. It is also great for farming, killing, and you can survive unlike characters like ryze or ashe that do great damage but are very fragile.

My first build, enjoy :]

Ignite

And

Ghost

Or

Flash

For 3x3, Flash is a suitable replacement for ghost, but i still recommend ghost and ignite for your primary spells, ignite allows you as many kills as possible for the expensive items, and Ghost is great for escaping so you can always be the biggest Around

Pros

Great Farmer
Heavy damage
High health
BIG

Cons

Primary target
Bad dps
Easy to kill with piles

Boots of Swifteness -
I almost always use these boots just because they give you the chasing/ escaping edge, And since your enemies wont want you to get max stacks for feasts, escaping is sometimes very important.
Rod of Ages - This item is practically made for Cho'Gath, It gives him ability power and enough health and mana for him to make it by the whole rest of the game.
Morello's Evil tome - This item gives you even more ablility power! It also provides good mana regeneration just incase your the spamming type, and Cooldown reduction which is AMAZING for Feast since you will do around 1200 damage with it in 1 hit and you want to do this alot (dont you?). A suitable replacement in case you cant manage to keep your feast stacks is the Gaurdian Angel.
Void staff - This item also gives you ability power(pattern?), not only that but magic penetration to when you see the big numbers from your spells you can count on them. It's important for all casters and if you've played one before you understand you this item.
Rabadon's Deathcap - Okay you're pretty epic now :], this item gives you the loads of AP!
Nashors tooth - This might be the item you don't understand, But you have to realize that Vorpal spikes only activate through melee attacks, and they do about 120 damage now, so in case all your spells are on cooldown, the 50% attack speed is something you can fall back on.
The 25% Cooldown Reduction is this items specialty, if you get enough gold to make it to your sixth item, you might be wishing your feast and other spells could always be ready to use, so with Morello's Evil Tome this item is just perfect! And of course another 50 AP is always good :P

I will try to add some photos in due time

For now, I can tell you i've gone 21/0 and I know i've gone 11/0 multiple times as well. I'm sure I can go further, but I dont take too many chances of charging head on so 21 is my record.

Like I said, I'll try to get you some proof soon so you can see the wonders with your own eyes.