Start off with Chainmail (which also gives AD because of Rammus' passive), then get giant's belt, then Sunfire. Just follow the order from there.

This build is meant for Twisted treeline, so using your starting money you can buy the chainmail, then quickly farm $ for GB just before lv 6. Once you get sunfire, everything starts going smoothly for you.

Use your powerball as an ambush is a great idea, and makes up most of your pre-6/pre-sunfire damage. Use defensive ball curl to pick off carries, or anyone who tries to harass with basics. Stay out of the way of abilities until you can charge with powerball, then use your typical E,W (and P later on) combo. Ganking half health enemies makes a sure kill, and so long as you can rush in, no one can beat you 1v1.

At some point once you understand the theme, you'll find that it gets too easy. Help in team battles with a taunt, or anytime someone tries to run away, and chase with powerball when able. Remember Ball curl gives good defensive, and Temors + Ball curl + sunfire = your best bet at damage.

Good luck!

~Onelastfrost