Not Updated For Current Season
This is intended as a jungling build. Warwick is all about survival of the fittest. Most seem to want to give him more dps, which is ok, but WW+Bloodrazors is more than enough damage, so by focusing on survival and blood scent, you'll be able to easily towerdive. Survive other junglers, survive ganks and rack up kills.
Try to keep your buffs up, the mana regen, CD reduction, ATK speed and slow really makes a difference during ganks, and you don't have much in the way of mana regen without them.
For the last item, I'd suggest either Bloodthirster for more damage, or Ghostblade for overall stats + maxed CD when you don't have blue buff. The extra ghost is nice too. You could go Guardian angel, but that's massive overkill imho.
Bring an extra hp pot and a ward if you fear you'll get ganked, drop the ward in the lone bush in between the two sides and stand beneath/above the spawn point until about 1:50 or until you see people in their lanes.
Switch veil and Omen build order if you're having issues with bursty casters/CC.