I posted on this earlier today in a WW items thread, but again I would state that WW players faced with his current kit sort of placing him betwixt AD/AP need to play around with the S3 itemization and maybe be a little crazy.
I like the suggestions that Imp previously laid out
Easy (good sustain): Build tanky. Spirit of the Golem (Jungle), Spirit Visage, and Frozen Mallet being good choices.
Medium (good dps): Build AS/On-hit: Spirit of the Elder Lizard (Jungle), Blade of the Ruined King, and Zephyr being good choices
Hard (good burst): Build AP. Spirit of the Spectral Wraith (Jungle), Malady, and Liandry's Torment being good choices.
I think that Twin Spirit is an interesting item for this iconic chaser champ if, again, you don't mind or can exploit the dip into AP building. And, being hybrid in damage output I don't think you can go wrong with grabbing Gunblade as one of your offensive items, especially if you are a player who favors Spirit Visage, which was just made better for WW imo.
There are a lot of trigger items out there that fit pretty well on WW, which is making me think about the 7.5% item trigger CDR mastery.
Basically, I feel like there's got to be a viable hybrid build out there for WW and I bet it's cozied up in mobafire or someplace else. I'ma check it