If you have a stealht summoner in the enemy team then you have to buy with the shoes a vision ward. Now if you have enough money go buy right away beserker greaves if you haven't then buy the dagger first. Make sure you get the first assist and get at least half of the kill money. If you're playing against magic people then buy Wit's End first. If you're playing against Tryndamere then buy thornmail. If you are playing against other melee then buy Frozen Hart. Now buy Nashor's Tooth. Now buy Phantom Dancer. It's a great item and gives you at ventage on enemy runners. Now it's time for the real work: Infinity Edge. Good attack and critical always helps and is needed so you attack much and fast. Now buy Madred's Bloodrazor. nice little magic damage extra. If you are lvl 18 then sell the Wit's End/Frozen Hart/Thornmail(If you think you can miss it) and buy Rabadon's Deathcap.

That's how i build DPS and more Ability Power to a 'Tank' champion.

Hoped it's usefull and comment for changes!

Have a Nice day and stay focused when playing LoL,

Greetings,
Farcrada