This is how I most commonly build Warwick. I've seen a lot of people build him using proc items like Wit's End and Bloodrazor, but with the recent changes to the jungle and masteries, I feel that an AD approach is more appropriate. Instead of doing 50/50 physical/magic damage, this build focuses on physical damage, and in doing so takes better advantage of penetration and life steal items. Also, since the jungle is significantly easier now, you barely even need the 1 health potion to start. I keep it in the build because you have money for it and you can use it instead of Q once to save mana before picking up blue. This also can help you stay in the jungle if the opposing team steals your blue, as Warwick can easily get manablocked early.

I use armor penetration runes, armor seals, and magic resist glyphs as a generic AD Offtank. I have considered running CDR glyphs and mana/5 glyphs as well.

Movement speed quints are very important as they assist you in getting through the jungle quickly and in executing ganks, which is your job as the jungler in the early game. These paired with the movement speed masteries allow you to get around quickly, dodge skill shots, and chase down wounded enemies.