So I play Warwick as a Tank/Dps and what you want to do with this build is to bring Warwick's Hungering strike to it's maximum by purchasing spirit visage to get more healing from it and sorcerer's shoes to get magic penetration to do more damage. So just harass the opponent by using hungering strike all the time to get them to lower health and then you can just jump them with Infinite Duress and hunt them down with Blood Scent.

Then you want to get the Sunfire cape so when you use Infinite Duress or just are in a meele combat you damage your enemy with Sunfire cape aswell as your regular attacks. You also get some basic armor from Sunfire cape to boost you in melee combat.

So after that you want to get some basic damage + attack speed and boost Infinite Duress by purchasing Black Cleaver because Infinite Duress is just 5 ordinary hits from Warwick and Black Cleaver lowers the armor of the opponent while you are punching him. Then you finish off with Bloodthirster to boost your lifesteal and damage even further.