Well, this sounds weird to most players (mostly because I'm still bronze) but i got cho'gath to level 7 with this playstyle. The way I got this was farming like you're nasus, but watch your positioning. Cho'gaths "e" can do a lot of dmg to champions while you are attacking minions. If your positioning is right, you should be able to hit your opponent with your spikes. That in combination with deahfire will do a lot of dmg. It's just insane if you try it.

While in laning fase, take your "e" first for so you can harras your opponent with spikes and deathfire touch while farming. When you have enough gold, or when you're low, go back and buy your catalyst of aeons. As fast as possible finish your rod of ages. After that: if you need armor, buy frozen heart. If you need mr, buy spirit visage. When you hit level 6, try to harras your opponent. If they are too strong, just farm and ult minions. Try to keep your ult when your jungler is ganking you, you need as much stacks as you can get and you can get infinite stacks from champions and epic monsters. Also try to help your team with dragon so you can get more stacks.

Late game will be like normal: just try to hit your abilities and ult whenever you can on a chamion (note* if you didn't know this: a small indicator will appear underneath an enemy when he's low enough to kill him with ult). When your team is doing baron, help them and kill it with your ult as your ult deals more dmg than smite so the enemy can't steal it.

If you followed most of this guide you will be good to go with this champion. He may not be played that much, but he can carry a team by tanking everything and doing dmg.

Good luck and have fun in your games. :D