Cho'Gath is one of the strongest tanks at LoL and is capable of doing good amount of damage as well. He can also farm incredibly good which is needed for this build.

For runes I choose Greater Quintessence of Fortitude, Greater Glyph of Focus, Greater Seal of Evasion, Greater Mark of Insight.

I choose Greater Quintessence of Fortitude because it helps a ton in the early game, giving you that extra hp to be aggressive and still stay alive.

Greater Glyph of Focus is great so you fast can get 6 stacks on your Feast. It also come in handy in big team battle mid and late game when you need to keep on the pressure with silence and knock/slow.

For seals I got Greater Seal of Evasion to compensate that I get boots of swiftness instead of ninja tabi. They also work well with my masteries as I get increased movmentspeed whenever i dodge.

Lastly I have Greater Mark of Insight to do that extra damage that makes Cho'Gath a treat forcing the enemy to focus you. These runes works well with the Archaic Knowledge mastery (15% magic penetration).

For items its important to get Heart of Gold so I can get as much gold as possible. I then go with Warmog so I can max the stats fast. After that I start building towards Frozen Heart which gives armor as well as allow Cho'Gath to be more aggressive. After that I choose Force of Nature and follow it up with Omen. I finish it of with Guardian Angel to help keep the stacks from the ultimate.

I pick Ignite as it is very effective to finish of enemy champions in the early game as well as in late game and Ghost so that you can catch up and finish of enemies with Ignite/Feast (also good for escaping as Cho'Gath wanna keep his stacks).

This build works out great for me but it has a weakness. If you are getting pushed back and having a bad early/mid game it is extremely hard to afford Warmog and Frozen Heart fast which can cost your life in mid/late game. Therefore is this build mostly recommended for players who play with a premade team and know they can handle early game fairly good.