Hi guys, welcome to this weird little guide for AP mid Cho'Gath!
I have had a lot of success with this fun pick in the midlane and I think more people should try it out :)
I admit it is an acquired taste (haha) and can be a bit on the slow side in terms of mechanics but the utility and sustain you get alongside the insane damage is worth it in my opinion.

Cho'Gath has some really nice AP scaling as well as great sustain and he gets a hilarious amount of health along the way. Most midlane champions are not tanks and most tanks do not do as much damage as typical midlane assassins or mages- Cho'Gath can be both which is amazing and pretty broken in the right hands.
If your team requires a tank in the late game then it is totally ok to switch your damage items for more defensive/tanky ones ;)

Firsty, his sustain in lane is actually so good. Farm up to heal up. Pretty simple and not usually hard to do especially once you get your first item.

His kit is full of CC (A knockup Rupture, a silence Feral Scream and a slow Vorpal Spikes!) and then his ult Feast really just frosts my cake and lays my bricks as it is an execute. It is possible to just go around and eat lower health champions when they're at half health which is insanely strong I think.

Feast can help your jungler secure objectives like drakes and baron as it can be used in place of a smite incase the jungler smites early or the enemy jungler is trying to steal it. Having him in the midlane instead of the toplane is especially helpful with this as you can roam and help with objectives without having to necessarily Teleport back to lane or risk losing too much XP and gold from minions.

Cho'Gath can also act as a defensive barrier by using his CC to protect fellow teammates and even set up lethal picks.

Also it is fun to watch him grow :)

Go on and have fun out there. If the enemy team are an annoying comp, you can take satisfaction from literally eating them and becoming a giant CC/Damage machine!

Pick your fights well and respect the champion's limits and you will be fine.

Thank you for checking out the guide and happy eating!