HI GUYS!

I made this for my friend who wanted to know how to play Warwick. And if you want some advise on good items at Warwick go read this! I play Warwick top or mid. I dont like jungle Warwick (or I do maybe just suck at it! :D) because he has weak ganks before lvl 6. And after the jungle changes is sustaining in the jungle not important (jungle Karma is possible). Have fun with Warwick!

Greater Mark of Magic Penetration you deal magic damage with Hungering Strike and Infinite Duress

Greater Glyph of Magic Resist you are a melee. And a melee can only do damage when he is close on the enemy. To get close you need to be tanky.

Greater Seal of Armor the same as the glyph. Reduce their damage or do more? Runes mostly changes the early game. And as warwick will "reducing their damage" runes be the best.

Greater Quintessence of Movement Speed because you chase a lot as Warwick

All items on warwick are situational. Take wits end before Glacial Shroud if you face magic dmg in your lane. I prefer starting with Frozen Heart and Wits End.

Frozen Heart:
Warwick has mana issues. This item gives alot of mana, CDR and a very good passive! (But don't get this item if you have Ryze in your team. He should buy this, because he scales best on mana.)

Wit's End:
This is a very cheap item, only 2000 gold! It gives you a lot of attack speed, which feels good. And it have a passive, that makes 42 bonus magic damage on your basic attacks. This bonus damage also work with your ultimate Infinite Duress!

The rest of the items are situational items. If you face hard physical damage, then buy armor. And if you face hard magic damage buy magic resist. If you are against a balanced team then get armor and magic resist items. And sell your Doran's Ring when you get that far in your build!
Why buy these items? Here you see a desciption of when you should buy the other items:

Banshee's Veil:
If you need magic resist is this the item, as the passive spell shield can defend you while using your ultimate (Infinite Duress).

Frozen Mallet - Atma's Impaler:
You will run and chase alot, the Frozen Mallet slow is good too! And these items give you alot of health, which is good when you have the role to be tanky in your team. And this makes your ultimate (Infinite Duress) to deal more damage as it scales on attack damage.

Madred's Bloodrazor:
This is good on your ultimate. Get this if you have another tanky guy who can handle the enemies, or if you feel that you are fed :3

Ionic Spark:
This item works on your ultimate and makes your farming faster. ONLY get this if you are fed and can handle the enemies easily.

Guardian Angel:
Good defendsive item.

Sunfire Aegis:
The passive works when you use your ultimate, as you are close to the enemies when using your ultimate.

Zeke's Herald:
Get this if your team have a strong Attack Damage/auto attack orientated team.

Bloodthirster:
People thinks this is a good Warwick item. But i don't like it. I havent tryed it on Warwick, because it is only a offensive item. And Madreds Bloodrazor is better when you want to be offensive.

Agressive Build:

I also reccoment this build if you are against a balanced team. Maybe get some defendsive instead of the Madred's Bloodrazor

Early-, Mid- and Lategame.
Early on should you use Q on your opponent very often. But always have some mana left. Dont spam it if the enemy also have passive lifesteal like Nasus, Garen and Mundo. But use it when you need some health.

When you get to the mid game should you use your ultimate on their carries to set them out of the game. But be careful to use it on someone with Quick Silver Sash, as they can get out of your ultimate with it! Spam Q on them while using your ultimate, because it cant stop your ultimate and you will use it as soon as possible.

Late game should you do the same as mid game. If you have a tanky jungler then go chase their carries in team fights. And your jungler will protect your own carries.

I am still working on this guide. My friend made me want to make a complete guide! So dont downvote yet. Tell me if theres something I could add to this guide.