Hi this is my first guide and I hope this build works for you :).I am not high elo player
But I am pretty good playing as yorick and i wanted share my build with you guys.

Greater Mark of Attack Damage I chose this rune because i know that you want do damage with yorick.
Greater Seal of Magic Resist Yorick needs more Magic Resistance
Greater Seal of Armor Extra armor is always good againts Ad Carries
Greater Quintessence Of Strenght More Ad

These Are Masteries that you need use

Summoner Spells that i use often

I chose flash because yorick dont really have escape skills.

Ignite for extra damage

Other Possibilities:

You can use this for escape or chasing

Survive little longer

I know this Is not long or good but i will make this better when i have time :)