Welcome to my build to Yorick.
I consider Yorick as an amazingly versatile initiator with this build.

Pros:
-Durable
-Mobile
-Fun
-Assist *****

Cons:
-Poor Farming
-Assist *****
-You hobble when you walk

Runes are as follows;

Armor Penetration Marks
-Why? Most of your skills including your ultimate do physical damage and most time in lane you ping with your E.
-Other options: AD


Mana Regen per level Seals
Why? Because Yorick is A LOT better with his ghouls out as frequent as possible, you need the mana to do so. Especially helps the laning phase.
-Other options: Health per level, Armor

Magic Resist Glyphs
Why? Simply put, it gives you a little more beef when you initiate a fight and helps greatly against casters who don't get hurt quite as much from your Exhaust.
Other options: Cooldown

Move Speed Quintessences
Why? 2 Reasons. Early on you need to be able to get in range for your harass to work and it helps a lot later when you are initiating fights.
-Other options: Health, Armor Pen, AD

Masteries are an awkward build of 11-6-13

You fill in the Offense tree until you reach armor pen...
Why? By filling it up to armor pen you get improved exhaust, even more crit chance in addition to your Ghostblade and Infinity Edge as well as even more CDR and then of course the armor pen to increase your damage output

...then you move to defense tree where you put only 6 point in both armor and magic resist...
Why?To increase your early game tankiness before you get your Banshee Veil or your Randuin's Omen.

...Lastly, you fill in the Utility tree to give you increased regen, experience and a shorter cooldown on your Flash
Why? The increased regen allows you to spam your skills even more so and adds to your laning strength while the experience boost is a no brainer and who doesn't like a quicker Flash? ^^

The item build above is the ideal, while this might now always happen I will explain other options as well as explaining the ideal

Ideal Build explanation

Philo Stone / Reverie
Why Philo Stone?
Adds to your lane staying power as well as gets you that much needed gold sooner, covering for Yorick's poor farming ability
Why Reverie?
The Reverie late games just adds to your initiation ability along with supporting your team and adding to your versatility

Ward
Why? Increases map awareness, helps stop you from being ganked.

Boots of Swiftness
Why? Allows you to get in range for your skills as well as run in to initiate. The speed also helps you keep attacking, you are melee after all.

Heart of Gold / Randuin's Omen
Why HoG? Helps cover for your poor farm as well as increase both you and your ghouls health, also a part of Randuin's
Why Randuin's? A versatile slow, much needed armor, even more CDR. Nuff said.

Phage / Sheen / Zeal ~ Trinity Force
Why Phage? Increases AD/HP for you and your ghouls.
Why Sheen? Boosts your damage output and buffs your Q a nice amount. Make that first hit count (:
Why Zeal? Movespeed for initiation as well as some nice attack speed.

Brutalizer / Ghostblade
Why Brutalizer? Increases your damage output and allows more spamming of ghouls :D
Why Ghostblade? Further increases damage output and gives you a hefty boost for either 1v1 fights, initiation, more damage output, or to escape.

Banshee Veil?
Why? Much needed magic resist along with a even more health for Yorick and his ghouls.


Other Options

Sunfire Cape - Adds more HP and helps further against AD as well as adding minimal damage whil you're in the middle of the battle.

Guardian Angel - Pair with your ult for a few extra lives (;

Many others, will be added soon.

Simple enough.

Max your E first,
Why? It helps more in lane than anything. Giving you a way to heal and a guaranteed harassment.

followed by your W (stopping for one point in Q and for whenever you can level your ultimate.),
Why? Slow is next line for how useful it is and most of the time it hits a high enough level to be useful right when you need it to be.

Lastly, level your Q
Easily the least relevant, put one point in early to gain a speed boost that can sometimes get you out of tight spots.

I personally favor Exhaust and Flash over any others for Yorick.

Flash - Allows me to chase/flee as well as assisting my initiation occasionally.
Exhaust - Keeps them slowed while the ghouls and Yorick beat their face in as well as gimps ADs and gives you the upperhand in most 1v1 fights.

Other options could include..

Ghost - Decent escape, chase. Keeps you on their tail so you can stay in melee range.
Ignite - Gimps healing (Great option if you see there's a Vlad/Warwick/Soraka/Etc. on the other team)
Cleanse - Against those cc heavy teams.