hi this is my second guide, I'm main support and Cho'Gath is one of my favorite Champions. He can be crucial when your top picks a non-tank champion. because as you expected you can go full tank.

i know it looks crazy but just try it

for many reasons
1. when you have an adc who deals damage you can go full tank.
2. lots of Feast opportunities because of the 2 champions you face, on ganks almost always one of them stays behind.
3. near drakes that you can consume with your Feast which spawns a lot more than heralds.
4. you can easily dominate bot lane if you have a good adc, your Rupture keeps enemies from escaping and your Feral Scream stops enemy combos which gives your adc a good time to get them to low health.

Pros

+ full tank makes you almost immortal especially when fed right (literary)
+ you counter most League of legends champions, mid to late game champions like Jhin, Darius, Hecarim and all AP champions become almost useless especially late game
+ sustain, on such high health your health regen will be enough to heal you late game and your passive is just too good for sustain
+ Rupture can stop enemies from escaping or stop attacks
+ Feral Scream can stop enemy channels like Urgot's Fear Beyond Death
+ even on full tank you make a lot of damage with your Rupture and Vorpal Spikes
+ very high health
+ a lot of people will think you're trolling

Cons

- Vulnerable to tank melters
- team sometimes leaves you alone thinking you can tank forever
- if not fed a bit you can have a hard time
- low mana early game
- a lot of people will think you're trolling

• On laning phase keep harassing with your Rupture but be careful of running out of mana
• use your Rupture for enemies who try to run (just a bit in front of them)or enemies who are following you
• use your Rupture for enemy jungler when they try to gank. you can almost always buy enough time for you to escape
• Save your Feral Scream for enemy channels or when you need a bit more damage
• your Vorpal Spikes has slow and good damage it's very useful on close distance
• DON'T be afraid to use your Feast on minions, you have 6, when no drakes are spawning soon and lane is stable use it on minions. sometime several minutes can pass without the opportunity for you to use it.
• Be careful of shield and healers/lifesteal it can ruin your Feast
• use your Flash for sudden appearance near enemy with low health for you to use your Feast

Hail of Blades- Is my go to option, combined with Vorpal Spikes it gives a nice burst of damage to get enemies to low enough health for you to use Feast. Predator is also viable, it gives you high speed towards enemy champion who is low on health and can secure you many kills good when choosing Goredrinker instead of Turbo Chemtank. other runes just useless, Grasp of the Undying gives you health but after many games i came to the conclusion that it's useless because the kills with your R that you can secure gives you is much much MUCH more health. also Aftershock useful for 2.5 seconds which is not much given you will stay in battle for much longer
Taste of Blood gives you much sustain on laning phase
Ghost Poro your sup item gives makes it easy to fill
Ultimate Hunter will make you spam you Feast which will give you much more sustain than Ravenous Hunter on the long run and you can get rid of the enemy making most damage
plus after a lot of experiments it's not as useful as you may think (33% effective on AWE)
rest is obvious