My first guide here hope you like it :)

Pros:
-strong late game
-good sustain early game
-good ganker after 6
-can chase down low health opponents with E
-insane AS boost with W
-
Cons:
-slow jungle cleaning
-weak ganks pre-6(that is why i take ghost)
-need lot of money for build
-early mana problems and blue buff reliant
-can accidentaly uncover gank if not careful

Primary spells:

Smite : Every jungler need smite! It is because it helps you clear buffs faster and gives you control over baron and dragon, so dont tell me that you dont need it. Just take it if you are going jungle.

Ghost : Reason i take Ghost is because it helps your early game ganks, but if you prefer Flash feel free to use it :)

Flash : Take it if you prefer it more than Ghost.

Secondary spells:

Exaust : Take it if enemy team has strong AD carry and if nobody in your team took it.

Ignite : If you love it.

These spells are best for Warwick but if you think that it is absolutely necesarry to take other spells,feel free.

You may ask why i dont take 21-0-9.Well it is because you NEED to share buffs with your team so if your AP carry is mana reliant give him blue buff(not at lvl 1 ofc.).
It is always good to have some health so you rush for Veteran scars in defense tree taking improved Smite, more armor and magic resist is never a bad thing :),
In offense you go for :

Summoner's Wrath : For improved Ghost.

Brute Force : Gives you AD that you need to clear camps faster.

Alacrity : For more AS

Sorcery : Because it lowers your cooldown which is great :)

Weapon Expertise and Arcane Knowledge : Some armor and magic penetration for your basic's and Hungering Strike

Vampirism : in combination with your passive it gives you lifesteal that you need for longer sustain.

Sunder : More armor pen for faster jungle clean.

Executioner it combines so much with your Blood Scent ie: Some (Un)lucky champ si running from you with less than half health. No problem!. You will catch them easily with your Blood Scent and Executioner will help you bring them down a LOT faster than usualy which is good for tower diving.

Take magic pen marks because it helps you Q deal more dmg
Take armor seals because it gives you nice amount of armor which helps you in jungle
Take MR per lvl glyphs because it is great late game where WW shines most
And at last take Greater quints of strenght for more AD to help you kill monsters faster.But if you take Flash take Greater quints of Swiftness to help your early ganks.

You dont have to rush maxing one spell first both Hungering Strike and Hunters Call are very usefull in jungle so if you max one spell quickly other gets weaker and dont help you so much. Take Blood Scent in lvl 4 and leave it there untill you maxed all other abilities, and ofc. take your Infinite Duress at lvl 6,11 and 16 but be carefull to dont ult target who has Quicksilver Sash.

Eternal Thirst : This passive is what makes Warwick great jungler, it is natural lifesteal and is reason why you dont need Wrigle's lantern

Hungering Strike : Awesome spell.Deals % of opponents max health or flat dmg if it is bigger ( To minions and monsters only flat)
and also it heals you. Great spell :)

Hunters Call : Awesome spell!Not only it provides you AS but it gives your team half of it bonus which is great if your team is AD mostly.

Blood Scent : Nice spell with extremly long range , it provides you Vision of opponent who is under 50% HP and also gives you MS which is always nice to have, it can even reveal stealth champions such as Akali who is realy anoying with her Twilight Shroud. Anyway great spell but better at higher ranks.

Infinite Duress : Your primary ganking tool it is also cool because it proc on hit effects such as your passive, Madred's Bloodrazor,etc.It is spell that makes Warwick unique.

Start with Long Sword and Health Potion.

As soon as you get enough money for Madred's Razors and Boots go back and buy it.

Than continue your jungle path(which i will talk later) and look for ganks.
After you got some kills and assists go back and buy Recurve Bow

Than Finish your Mercury's Treads or Ninja Tabi if enemy has right-click-to-win champs such as Trynd or Yi or if they have fed AD carry.If enemy team has no CC(what is realy hard to happen) take Berserker's Greaves

Than you want to complete your Madred's Bloodrazor because it helps you take down tankier enemies in mid-late game.

After that you want to buy Giant's Belt and Chain Vest

Then buy Warmong's Armor which is great item on WW and you want to finish Atma's Impaler because you have lot HP and this give you AD based on your max HP.

Take Randuin's Omen if enemy have fed AD carry or if enemy have fed AP carry feel free to take Force of Nature.

Right now game is very late so you will need more sustain so take The Bloodthirster to help you heal more and increase your dmg output or switch with Banshee's Veil.

Other optional items:

Guardian Angel This item is good if you need mixed stats, it provides you nice amount of Armor and MR and also have AWESOME passive if which is if you die you get resurected and have 750 hp and 375 mana back what is great if you are only in your team and there is only one enemy left waithing for you to resurect and you have your ult ready just pop it and kill him while he is raging in team chat while you push enemy towers :D

Thornmail Gives you most armor in game only buy it if their right-click-to-win champ is fed hard. All you need to do is stand and watch them killing them self .

Frozen Mallet Buy it if you need to slow enemies down because they are always running away. This item will get smile off their faces . Combined With your E it is great .

Wit's End Very good item on Warwick,scales well with your ultimate giving you bonus dmg and stacking MR,nice item overall take it if you feel you need it :)

Note: i took this picture from another build so dont think that i am saying it is mine


You can go 2 routes :
Blue buff->Wolves->Wraiths->Red buff->Double golems
or
Wolves->Blue buff->Wraiths->Double golems->Red buff

First of all Warwick is not fast jungler! so in 1st case you can go to red as soon as you finish wraiths because Smite will almost be off cooldown, than proceed to double golems and look for gank.If you are at blue side go gank mid or bot, if you are at red side gank mid or top. If all lanes are pushed continue jungling and consider counter jungling.

ALWAYS use Smite when red or blue buff are low enough to kill.
After successfully ganking mid or bot lane ping your team to go for Dragon.It is VERY important to kill dragon at least 1 time after 20 mins.Dragon kill proved gold for your whole team!Each of your team mates gets 190 gold which is 950 global gold.You MUST smite Dragon and Baron to protect from stealing.

You need to buy ward !They are cheap and everyone can afford them. Dont count on your support to ward Dragon and Baron YOU CAN DO IT TOO.Wards are life saviors worth only 75 gold(125 for Vision Ward which detects stealth objects and champs).

In team fights you NEED to focus squishiest targets because they are usualy carries and supports. You are tanky enough to initiate but dont do it with your ultjust walk, activate W and start ripping enemies appart with basics and Q , only use ultimate when you are shure that enemy with CC are or dead or have their spells on CD.
If you have enemy Teemo blinding you while ulting bait him to use it on you buy pretending you are going to ult someone and Teemo problem solved. if you go 1v1 with him wait for blind to end than just ult him and almost kill him only with it and Q. I gave Teemo special part here because he can be very lethal to you and you need to focus him if he play AD carry.If in team there are Strong AD carries focus them or exaust them if you took it and AP carry is bigger threat to you. Than go for that AD carry who is or dead or still exausted because you need 2 sec to kill AP carry(except Ryze he is little more tankier than normal AP's). With finished build you can do solo Baron quite easy, and if some foolish enemy come 1v1 to you or even 2v1 you can beat their ****** easy because of your ridiculously large lifesteal and tankiness.

This is my first build on MobaFire so please have that in mind when you vote on this and also i apologise for small amount of pictures so please dont be too hard on me .Let me know what do you think and should i add something :)
P.S. Sorry for typing errors :)