i myself build cho'gath ap jungle, but use the standard ad rune page to start with. i have found that the armor and extra ad help at low levels to dominate the jungle, but this is just me.

this is obviously centered around a jungle cho'gath so you will obviously need smite. i myself like exhaust for ganks because it can help when you need to run, or miss with the q on a gank. ghost, surge, ignite, flash are the other ones i would recommend over the other spells.

this cho'gath is insane if done right. i start with my q then a leash blue and smite to kill the golem. next i get my e, go to wolves, then wraiths, then small golems (pop your health pot as you start the encounter here). after this, get the w and start to get red buff. smite should be up by now. get red then gank bot/top depending where u start. sit in the lane's river bush and land a q. next, run in and silence and murder them. having a good team is essential to getting the kill here and if you die, then you are severly set back. if you live, now would be a great time to gank. next go back into jungle and go crazy from there. once level 6, get your ult and go gank to get a feast stack. after, go into the jungle and go crazy yet again. keep gaining feast stacks. try not to initiate team fights but run in, q to knock up, w to silence, and auto attack until slow wares off. at this point, if they are low enough health, ult for the kill!!!

you may not have cared until now, but cho'gath has an op passive. when he kills a unit, he gains "x" health and "x" mana. so while jungling, if you for some reason get low on health, go kill the wraiths or wolves because even the small wraiths/wolves give you this set amount of health.
*NOTE* THIS AMOUNT INCREASES PER LEVEL.

the items here are essential to getting this right. after the first gank, make sure you have atleast 700 gold before you b back or you will not be able to get what you need. you start with the +20 ap tome and here you buy boots and a kage's pick for the gp5 bonus. next i don't b again till i have 1350 minimuim gold so i can get the catalyst of the protector. from here, the guide should explain better than i can.

pros:
great start pattern
gives lots of ap
good late game if successful ganks at start
ult does true damage + ap damage
great at initiating ganks
assists work just as well as kills do so no worry if you dont get kill from gank

cons:
q is skill shot
build not good if not fed kills/assists
hard to kill when ganking people with full health