All you need to know. In one section!
Cho'Gath is not really a tank... just cause he gets big doesn't mean you have to build tanky. The only tanky item I opt for is Rylai's, mostly because of the slow. I usually get this on any mage build because it helps with chasing people with higher move speeds because most mages are 305-315. It also provides extra health so you don't get 1 shot. Other than that Cho is a mage. A full on mage. He has some of the highest burst I have seen on any champ. And his spikes are great for pushing through minions. Build some AS to get it to proc more often and you are set. Malady is really good for the attack speed but it also gives magic reduction and a bit more on hit dmg. The Lich Bane will make your basics hit pretty hard as well as that pesky move speed for those 330 champs with PD. The beserkers greaves are a personal preference with him. I also go for the sorcerers shoes if the team is more tanky. I have just found that the attack speed really helps with pushing a lane. If the team is already really squishy and isn't building magic resistance (which they should be if you are scary enough) skip the void staff and grab another AP item like the unholy grail. Provides great mana regen and cool down so you can chomp more and sustain longer.
That's pretty much all I got for Cho. Takes a sec to get used to but when you do, it's really fun.