This is my build towards a jungle Warwick. Warwick, in my opinion, is one of the best Jungle Champions in the game. Due to his very own life steal and his increased attack speed.

Warwick, for me, has always been a very cool champion, He looks awesome, and when you play him well, you feel awesome.
Warwick is also an amazing initiator, his ultimate can lock onto the enemy carry and deal a major amount of damage to their health. With this damage being dealt and them being suppressed you team can easily kill the carry and do a significant amount of damage to the enemy team, once you recover from your ultimate, you can run in with Hunter's Call and Hungering strike.

Warwick is also by far one of the best chasers in game.
With his blood scent activated he can see enemy champions and it also grants him increased movement speed, I for one get annoyed when you are chasing an enemy and the disappear into Fog of War when you could pick up the kill. But with Warwick, this problem is no longer there, YOU CAN STILL SEE THEM!

Another experience I had with the advantages with blood scent is that a Jax thought he could be clever and sneak behind to get a kill, whilst I was killing dragon I could see him as he was below 50% health and easily picked up the kill.

For runes, I usually go for Armor Penetration marks and Quintessences, Attack speed Seals and Cooldown Reduction Glyphs.
The armor penetration will help you kill the bigger, harder jungle monsters, the attack speed increase your lifesteal capabilities and the cooldown reduction allows you to spam your Q

This item build, I always find, helps a lot during Jungling and Late Game. Once you get Madred's bloodrazor, team fights would be easy, you can focus down the tank thanks to the passive, or you can help pick off the weaker ones. The passive of Madred's bloodrazor goes beautifully with attack speed, as each attack deals 4% of their maximum health in Magic Damage.

With the lifesteal and Damage of The Bloodthirster, you would survive team fights and deal a lot of damage whilst you are at it.

My god, Jungling is amazing with Warwick, as soon as I got him, I jungled. In the past, I have to admit, I was a failure at jungling, I had tried with both Olaf and Nunu, but to no prevail.

My Jungling route is always this:

Duel Golems
Wraiths
Wolves
Blue Buff
Red Buff
Back
Then I walk around in their jungling killing everything.
GANK TIME!

PROS!!!:

AMAZING JUNGLER!
Insane damage late game
Great initiator
One of the best chasers

Cons:

Easily targeted
Under leveled early game
Useless Ganker below level 6