Welcome to my Cho'gath Build.
This is my first Build on Mobafire. So if it is not that good, please give me some Tips. I know that my English is not good :D , but i think it is enough, that you can understand my Guide ;).
So lets start.

Pros:
- Cho'gaths ultimate is very good to get life, so you dont need to buy Warmog's Armor or something like that.
- In my opinion, Cho'gath is ungankable. When somebody ganks you, you can easily run away. With Boots of Swiftness , you're so fast with Cho'gath and with his W Spell you can silence the champion who want to gank you, so he cant cast a spell.

Cons:
- Cho'gath needs a lot of Mana. But it isn't a Problem, when you have a good Mana Regeneration.

We start with Doran's Ring , because Cho'gath needs a lot of Mana. Doran's Ring gives 5 Mana every 5 seconds (1 Mana per second). After Doran's Ring we are going to buy Boots of Swiftness, cause that gives you a lot of Movement Speed and this Item is good to escape ganks. The next Item is Catalyst the Protector, because when you get Level up, it will restore 250 health and 250 Mana over 8 seconds. After Catalyst, we are going to buy Glacial Shroud. With this item we get 45 Armor and 425 Mana and this item will reduce our Abilitys by 15%. The next Item is Force of Nature, this Item will give us 40 Health every 5 seconds, and will give us a nice Magic Resist. Our next item is Frozen Heart, because this item will give us 99 Armor and 500 Mana. This is good, if you play versus AD Champions like Xin Zhao or Tryndamere. After Frozen Heart we buy Abyssal Mask, because this item give us some Ability Power and Magic Resist. It also reduces the Magic Resist of nearby enemy champions by 20. Our next item is Banshee's Veil. Banshee's Veil gives us Magic Resist and Mana. This is good, because you can stand a long time on the lane. Our last item is Guardian Angel , because it revives you're champion upon death (BUT!! This Effect can only occur once every 5 minutes). I took this Item, because you don't loose your ulti stacks, if you are revived.

Our Masteries are 9/21/0. I chose this Masteries, cause in Defense we got Magic Resist and Armor. We also get Health and Health Regeneration, Movement Speed and Cooldown Reduction. It is important to have Mana Regeneration with Cho'gath, cause he needs lot of Mana. So we got 9 in Offense, because there we got some Ability Power and Cooldown Reduction.

My Runes:
Greater Mark of Armor
Greater Seal of Replenishment
Greater Glyph of Scaling Magic Resist
Greater Quintessence of Ability Power

Greater Seal of Replenishment is important for a good Mana Regeneration

With Cho'gath i upgrade the Q Spell first and then E and W. I max the Q Spell first, because it's a good Spell to attack and makes a lot damage. I look that W and E is balanced.

I chose Flash and Teleport.
Flash, because you can easy flash away.
Teleport, because as a Solo Top you need Teleport if somebody rushes you're lane.

I hope that you can understand my Guide. It will be great if you leave a comment below, and tell me what is good and what is bad. English is not my mother language, so please dont take it that hard, if i have some grammatical mistakes.
Thank you for reading this guide and don't forget to rate this Build.

Best Regards,
Ghost