This build isn't yet tested in game.
The idea is to build attack damage / magic damage 50%/50% Warwick, with big attack speed.

I will use Malady and as the Wit's End item has changed during latests patch!
Also this way Warwick ultimate could be useful, as it strikes 5 attacks in short time 1,7 sec and applying quickly items (Wit's Ends and Malady) passive.

So the magical damage from items will be 20+42=62 magical damage each hit (after 4 stack of-course).

Plus after three hits Warwick will gain 4*6=24 reduced magic resistance on enemy and increased magic resistance equal of 5*4=20 so you have 9 magic penetration from runes and 24 magic resistance reduced from your Malady stacks.

Also you gain 9 AP from your runes and 10 AP from Ignite it Offense skills (Burning Embers). Also you gain 25 AP form your Malady that's 9+10+25=44 AP and your spell Hungering Strike will have +44 magical damage boost of Warwick's AP rate on this spell.

Core item cost is equal of 4745g. in further items I'll update this testing build.

Added item Madred's Bloodrazor Nice item that deal 4% of max health in magic damage, maximum of use in late game, could be useful mid-game too.
4745+3800=8545g Junglers core build on 5v5.

Added 2 items more:
The Black Cleaver (armor penetration stacks 4 times)
Sword of the Divine (100 magic dmg every 4th hit)