Warwick: Did I scratch you? Is a build I have designed that helps me do well. I was a noob to WW and I kind of mashed together some builds and some failed, and this one really clicked for me. I usually get around 17-25 kills and 1-4 deaths with this build.

Greater Mark of Magic Penetration Most of your damage done with this build is magic damage, so let's add this to make us do more!
Greater Seal of Evasion It's a possible life saver, very handy in 1v1's giving you a good dodge chance can give you that much more of an advantage.
Greater Glyph of Cooldown Reduction The cool down reduction provides an advantage in fights and ganking.
Greater Quintessence of Magic Penetration Once more, most of your damage output is from magic damage, so let's give you more.

Exhaust I choose this because when you get an enemy to low health and your Blood Scent makes you run faster, why not make him run slower and get an easier kill, rather than him/her make their escape?

Ignite I chose this, mostly because if your exhaust is on cooldown and your enemy is really low on HP and it's a champion like Master Yi who can use Highlander and just run, he'll have that Damage Over Time and it can kill him.

PROS:

High amounts of damage
Easy to 1v1, occasionally get an easy 1v2 with squishies.
Massive lifesteal

CONS:

Kind of easy to kill
Can die alot if you don't know how to play WW