This is my first guide. I don't expect it to be good, but you could give it a try. It's a nice build that focuses on the synergy between Cho'Gath's Vorpal Spikes and on hit items like
Malady and Wit's End.

I take 9 points in offense so i get the bonus attack speed and armor penetration that will help you later on and 21 points on defense because a bruiser without armor, health and magic resist won't survive to long :3.

Greater Mark of Attack Speed These runes are very useful on Cho' Gath early because they contribute a lot at his damage, giving him an edge in dueling.

Greater Seal of Armor Standard runes for tanky bruisers. Helps you take less damage from minions, in ganks and trades.

Greater Glyph of Magic Resist Now the reason i don't take scaling is because you have enough magic resist from the build. You need this chunk of magic resist early on so you wont be vulnerable against magic users.

Greater Quintessence of Movement Speed These are extremely valuable on Cho Gath. Not only it makes him get our of tight situations easier but it also make him less kiteable. They are mandatory.

Boots and 3 Health Potion. These will help you move faster so that you can keep up with your lane opponent and escape ganks.

If you're under heavy harras from the enemy, take Null-Magic Mantle if he does alot of magic damage or Chain Vest if he does alot of physical damage. Again all you need to survive.

Mercury Treads - unless the enemy has more than 3 Physical damage dealers. This will soak up magic damage and reduce the time you will be cc'd by the enemies. If the enemy has no cc or casters, you can buy either Ninja Tabi or Berserker's Greaves

Malady - This synergyses with you Vorpal Spikes, making them do more damage, increasing your attack speed and doing 20 damage of its own.

Phage - Self explanatory. Health, damage and a slow.

Wit's End - This will give you a nice boots of attack speed and damage and will also make you endure more magic damage.

Frozen Mallet - Same as Phage but much much better. Unlike Phage this item gives you a 100% change to proc the slow, making it extremely hard for the enemy to escape you.

Atma's Impaler - This item is incredibly good in this build because not only it will make you more tanky than you are, it will also give you 2% of your healt as attack damage. That is alot on Cho'Gath because he has high base health, gains health through his stack from his ultimate and also from Frozen Mallet. The critical chance is also helpful.

Guardian Angel - A free get out of jail ticket. In team fights you will take a lot of damage, this item will help you soak it up. What make this item so good is its passive. It will revive you after you fall without losing any stack from your ultimate and thus you can continue to kill your enemies or escape them.

R>E>Q>W

Carnivore (passive): Whenever Cho'Gath kills a unit, he recovers 32 + (2 x level) health and 3.25 + (0.25 x level) mana.

This is one of the best sustain abilities in the game. This can make the difference between life and death sometimes. It will also make your opponent think twice before attempting to trade blows with you.

Rupture: Ruptures the ground at a target location. After a short delay (0.75 seconds), enemies are launched into the air for 1 second, dealing magic damage and slowing them by 60% for 3 seconds.

Gives you a way to disrupt enemy junglers that attempt to gank you, cc an enemy that attepts to flee and even helps you farm.

Feral Scream: QUIET! Cho'Gath screams in a cone in front of him, silencing enemies for a short period and dealing magic damage.

Not realy sure what to say about this one. Good damage, a nice cc and sometimes can save your ***.

Vorpal Spikes: Cho'gath's physical attacks launch spines which deal magic damage in a line in front of him.

This is the bread and butter of this build. It does so much damage when coupled with attack speed its one of the best abilities in game in my opinion. This also synergyses with your passive and is one of the best farming tools.

Feast: Devours an enemy unit, dealing true damage (1,000 to minions) that ignores armor and magic resist. If the target is killed, Cho'Gath grows, gaining extra health (max 6 stacks). Cho'Gath loses half his stacks (rounded up) upon death.

This ability is just insane. It does immense amounts of true damage. If you kill your target it will give you a stacking buff that increases your health. Stacks up to 6. If your lane opponent went back use it on minions. If not keep it in case they make the mistake of taking you 1v1. Try to finish them off with it.

Flash: Meta :3. Flash to safetly, flash to finish an enemy, flash cuz you can.This is the best summoner for any kind of role. It will save you a lot of times and will also help you secure the kill on that running Teemo.

Exhaust: In this build Cho'Gath is vulnerable to kiting early on so make sure you grab exhaust so you can slow your enemy. It also helps in case the enemy jungler tries to gank you and also if the enemy does alot of damage in a trade. I can't remember how many times this saved me or helped me secure a kill.

Alternatives

Ghost: This is a good alternative for Exhaust as it will provide bonus movement speed so you can catch your opponent. Still I personally find it lacking, thus i take exhaust.

Ignite: If you feel you're fast enough, or you want to make sure you don't get outsustained by your lane opponent feel free to take this instead of Exhaust.

Surge: Attack speed, ability power and makes Cho even bigger that he is. A good alternative for Exhaust if you think you'll need it.

Teleport: Good for ganking other lanes when your lane opponent has left his lane, also good for returning to your lane after you went back to buy and will also let you help your team secure a map objective ex: Dragon, Enemy buffs, etc.

Bad

Heal: You have enough sustain and you are very tanky. Why would you need it.

Clarity: You get mana via your passive. This is not good for you.

Promote: Bad. You are already a pushing machine. You don't need more pushing power.

Smite: You're not a junlger. Just don't.

Revive: "No wait on death? Cool" No it's not. With a 9 minute cooldown i don't even know why this summoner is in the game.

Cleanse: Not realy worth taking it as a summoner on Cho. If you realy think you need a cleanse just buy a Quicksilver Sash instead of a Guardian Angel.

Clairvoyance: Support summoner spell. Won't help your lane too much. Not realy worth it.

It's a very fun build. Try it :3. Feel free to comment and vote. Sorry for the lack of images and such. It's my first time trying to make a guide so i don't know all the tricks yet. That's been said, Good luck and Have fun!