As u know, season 8 is more of a tank season. Most tanks do very well, both in lane and in teamfights, providing both massive damage and tank. Likewise, Cho'Gath is very tank and has a huge burst damage from Feast. He also provides much cc with knock-up from Rupture and silence with Feral Scream. Not forgetting that Voral Spike zoning enermy top laner from CS and losing health when standing behind minions.

Runes are shown above. Its really simple. It provides tank, sustain and also a shorter cooldown on your ultimate, Feast in order to use it more often during teamfights. The stacks are really important.

Remember to use your ultimate whenever possible on the enermy. The stacks gives Cho'Gath massive increase in health and range. Remember, Feast can also be used on minions and monsters, use it wisely can help u steal a dragon or baron (it may not be easy). There is not much out there for Cho'Gath. Just remember to use Rupture properly as cc for capturing and escaping, as well as silence from Feral Scream to prevent champions like Nasus and Tryndamere from ulting before you do to secure the kill. All the skills cause quite a lot of mana during early game, so use them wisely during trades.