He doesn't have lifesteal in his kit unless someone runs grasp of the undying. He has sustain through his passive (killing minions). Cho'Gath players are all over the board, some are really good others are terrible. His silence is the only reason he is incredibly strong because the duration and range gets further the more points he puts into it. His knock-up is terribly telegraphed and only easy to land if the enemy is silenced first.
He is a sort of a "fake tank" too since more Cho'Gath have mix builds and don't go full resistances. He is versatile, but easily kited and if he gets caught out and dies he loses his stacks and gets weaker.
He is just a burst mage that can be somewhat tanky that offers some team utility if he loses lane. He is almost like a juggernaut, easily kited but can deal damage if you get too close or misposition.