Yorick is a attack damage with a splash of ability power champion that is very underestimated. With this underestimation you use it against them. and completely destroy them. This Yorick build could also be used to play mid.

-Pros
*People will run from your omens
*omens will do a ton of damage
*EPIC SUSTAIN!!!
*Yorick is a little bit tanky

-Cons
*Yorick doesn't have a good running spell except W and Q (in that sequence)
*is VERY mana hungry with out manamune
*W is scaled off of ability power and is mostly used as just a slow
*if ultimate isn't used correctly it can be wasted

*Last hit, and use your W for the A.O.E
*Save your E for being ghanked or brought down by champs or siege minions.

Your fifth item is a situational item, which means that if you don't need the armor, get health or extra damage.