Welcome to my build of Yorick - The GraveDigger... Please comment after guide ;)

Runes Build:

Mark Runes: Buy Greater Mark of Magic Penetration for more magic penetration because 2 of your important skills deals magic damage

Seal Runes: Buy Greater Seal of Armor for more armor to be more resistant to damage. Its little but again is something...

Glyph Runes: Buy Greater Glyph of Magic Penetration to benefits your Omen of Pestilence and Omen of Famine skills with magic penetration

Quintessence Runes: Buy Greater Quintessence of Magic Penetration to benefits your Omen of Famine and Omen of Pestilence skills

Masteries:
My masteries are 27/0/3 to benefits my skills.

Very important mastery skill is Arcane Knowledge . This will penetrate 10% of your enemy's magic resist.

Other important mastery skill is Sunder . This mastery skill ignore 6 armor from enemy's defense.

Its good to upgrade Weapon Expertise for 10% armor penetration for you Omen of War skill and your normal attacks

I upgrade all ability masteries to buff a bit my Omen of Pestilence because all of my items are attack damage items

Items:
First start with Sapphire Crystal to have more mana. After that buy Meki Pendant. After that finish this item to Tear of the Goddess

Second items is Ionian Boots of Lucidity. With this item you will have more big cooldown which will low your skill's cooldown. Other type of boots which you can buy are Ninja Tabi. This will gain you defense and dodge rate ...

Your third item is Manamune. You finish this from Tear of the Goddess to gain mana, mana regen and attack damage

Your fourth item is Black Cleaver. First buy B. F. Sword . After that buy Dagger. Finish it to Black Cleaver

Your fifth items is Bloodthirster. First buy B. F. Sword . After that buy Vampiric Scepter. And finish it to Bloodthirster

Your sixth item is Infinity Edge. First buy B. F. Sword . After that buy Cloak of Agility . Finish these items to Infinity Edge

Your seventh item is Spirit Visage for more health points and cooldown reduction. Dont forget about magic resist. You can buy this item on the beginning of the build or in late game depends on you and your enemy team.

Skill Sequence:
First upgrade skill W Omen of Pestilence because it deals high damage on low levels and slow enemy.

Second upgrade skill E Omen of Famine because heals you with 40% of damage dealt

Third upgrade skill Q Omen of War because it deals damage and if somebody wanna kill you while you are on low hp you can increase your move speed by using this skill on enemy.

Try to upgrade more W Omen of Pestilence skill because it deals high damage. Depends on you, you can upgrade more E Omen of Famine

On level six upgrade your ultimate skill Omen of Death and be careful in team fights. Use this skill on your core player or in 1 vs fights use it on you to increase your damage.

Upgrading of skills depends on your playing style ... this is mine :P

Summoner Spells:
One of your summoner spells which you can take is Ignite but this is not so important

Other summoner skill which you can take is Flash . This will help you to escape from somebody or to get enemy.

Exhaust is one of the skills which you can take. 1vs1 battles you will own with this skill or if enemy try to escape from you, you can use it buy W Omen of Pestilence too slow him and your enemy's chance to escape is less than 10% :D

Heal You can take this skill if you cant without it...
SKILLS WHICH YOU NEVER HAVE TO TAKE:
1. Clarity This is useless with Yorick
2. Cleanse This is not so important. I never use that summoner skill
3. Clairvoyance ...useless. Let's supports take this skill
4. Smite ...No need you, this is for jungleres
5. Teleport This no needs you the are better skills than this ...
6. Rally This give you low damage so its not for you
7. Revive This skill is not so important
8. Promote This skill actually in not so useful for me but is very nice for backdooring of the minions :D This minion will push so much :D

So that from me for Yorick. Now its your turn to try it ... If you want comment below the guide.