Just Found Out The Wonders Of Cho'Gath.

Any tips for me?
I just started playing him the other day: http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/1736733822/206176227?tab=overview

and then again today: http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/1737124046/206176227?tab=overview

So in the first game i didnt know what to do and built a Rod first (albeit the wrong way lol i started with a blasting wand because i wasnt thinking; dem noob mistakes) and found it to be a pretty good start on him. So i tried it again today (this time the right way) and found the my build works pretty good, but obviously im just following the recommended items except for ROA.

If anyone wants to look at my item builds and tell me what i should be building first and what i should be building in certain situations that would be most appreciated. Also what summoner spells should i take? Teleport has its uses but i was also considering taking Ignite and then trying out Ghost afterwards. Also what champions match-ups does he tend to struggle against and which ones does he destroy? After 4-5 more games i intend to take him into ranked as my AP top choice.

Thank You for any advice :)