Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
GIANT MAN !!!
I chosed Thornmail at first item because Thornamil give nice armor to the start of the game.
Next i choose Boots of Swiftness because he gives nice Movement Speed.
After Boots of Swiftness i buy a Force of Nature, because he give nice magic res and Cho'gath need it.
Next i buy a Guardian Angel because, Guardian Angel have a nice passive and Guardian Angel give armor and magic res.
After Guardian Angel i buy a Warmog because Warmog give a nice heal.
To final item i buy a Force of Nature again because to the last is nice.
I choose Armor and Magic Resistance to have more power with Cho'gath.
The health runes to have more health.
I choose Ghost to run when enemys try to gank you.
Ignite is nice to firstblood because if the enemy is running with 100 hp with the Ignite you can kill him.