Mercyleess here, in this guide I'll note and show you how I build tank Cho'Gath.

My runes are specialzed in early resists and health so you can stand in lane a little bit longer and farm minions with Vorpal Spikes

Mesteries I use are focused on survivability and regen and that little bit of extra experience that will help you get your ulti faster, farm your ulti and maybe get a kill.

My item build focuses on fast HP gaining with late armor and resists, with that way of build I'm more durable especially if my ultimate has all 6 stacks.

If someone from your team fed enemy carry(s) or they have more than 3 of them you MUST exchange Force of Nature for Randuin's Omen or Frozen Heart.

I use level rupture and feral scream to deal more damage with putting one ability point in vorpal spikes at level 4 to make farming minions much easier and you can kill even few instead of one minion with that ability.

I use fortify since I am tank and that extra damage allows me to farm minions more effectively and can save turret or teammate's life if enemy tries to turret dive. I also take teleport becouse with it you can teleport to friendly minion or even ward behind enemy lines, gank or even clear a lane that filled with minions and get some extra gold.

Pros

enough mana and health due to passive
nice damage in early game if you farm properly and have mana
good at quick finishing off enemies with ultimate
great tank
excellent farmer
tons of HP

Cons

long cooldowns
quickly out of mana if not farming minions with passive
ultimate's stack dependant until late game