(Outdated, update coming)Hi my summoner name is Slappiz and I play Yorick mainly in ranked.
This is my build.

I'll add more content to the guide when I get some positive or negative feedback.

Ignite: Because it synergies really good with W and E. Having about the same range as E and is a great finisher during laning phase.
Really good endgame to vs those unkillable Tank Warwick and Swain.

Flash: I don't really think a explanation is needed but...
Flash I take for survival or sometimes for reaching that last hit.

Omen of War
(Active): Yorick's next attack, in the next 10 seconds, will deal bonus physical damage and summon a Spectral Ghoul.

The Spectral Ghoul deals additional damage and moves faster than the rest of the ghouls. While the ghoul is active, Yorick moves faster as well.
Cost: 40 mana

Cooldown: 9 / 8 / 7 / 6 / 5 seconds
Bonus Damage: 30 / 60 / 90 / 120 / 150
Ghoul Extra Attack Damage: 8 / 16 / 24 / 32 / 40

Bonus Movement Speed: 15 / 20 / 25 / 30 / 35 %

Omen of Pestilence
(Active): Yorick summons a Decaying Ghoul that arrives with a violent explosion, dealing damage and slowing nearby enemies for 1.5 seconds. While the Decaying Ghoul remains alive, nearby enemies continue to be slowed.
Cooldown: 12 seconds
Range: 600 (estimate)
AoE Radius: 200 (estimate)

Cost: 40 / 45 / 50 / 55 / 60 mana
Magic Damage: 60 / 95 / 130 / 165 / 200 (+0.8 per bonus attack damage)
Explosion Initial Slow: 20 / 25 / 30 / 35 / 40 %

Ghoul Ongoing Slow: 10 / 12.5 / 15 / 17.5 / 20 %

Omen of Famine
(Active): Yorick deals magic damage and heals for up to 50% of the damage dealt. A Ravenous Ghoul is summoned behind his target, which heals Yorick for the damage it deals.
Range: 650 (estimate)

Cost: 55 / 60 / 65 / 70 / 75 mana
Cooldown: 10 / 9 / 8 / 7 / 6 seconds
Magic Damage: 55 / 85 / 115 / 145 / 175 (+1.0 per bonus attack damage)

Omen of Death
(Active): Yorick conjures a revenant in the image of one of his allies that will have a percentage of their max health and attack damage. The revenant lasts for up to 10 seconds. If his ally dies while its revenant is alive, the revenant sacrifices itself to reanimate them temporarily by restoring them to full health and give them time to enact vengeance. The reanimation will last for up to 10 seconds.
Cost: 100 mana
Range: 900 (estimate)

Health and Damage Percentage: 50% / 75% / 100%
Cooldown: 120 / 105 / 90 seconds

Just an intresting thought, Yorick with Innervating Locket?
And available item, Yorick with Tiamat?

Reason for item purchase
Manamune: Yorick is a skill spammer and he has mana problems. Manamune is fairly cheap and is by far the best dmg item on Yorick.
Spirit Visage: Health, Magic resist, CD reduction and increased healing for your E skill. This item is ment for Yorick.
Sorcerer's Shoes: The E and W skill are magic damage and the extra magic pen from the boots really boosts your burst on squishy targets.
Atma's Impaler: Great dmg boost togther with Frozen Mallet. And the armor is enough to make you feel tanky endgame.
Frozen Mallet: Synergies good with Atma's Impaler and the extra dmg and the slow really help killing the enemy teams carrys.
Banshee's Veil: For Magic resistance and the extra Hp and Mana boosts your DMG.

Pros
- You will end up with about 260-290 Attack Damage endgame (300-330 with Nashor and elixir).
- 3300 Hp
- 140 Armor and 145 Magic Resist

Cons
- No Lifesteal ?? I don't really know.. I belive the gear is enough to Survive a TF while killing the enemy teams carrys.
- No armor pen. Well tbh you will do tons of damage anyway. You are not ment to take the tanks down and your carry targets aint stacking armor or magic resitance.

Greater Quintessence of Strength: Good dmg boost at low lvl, easy last hits and better harass
Greater Glyph of Warding: Squishy early game
Greater Seal of Resilience: Squishy early game
Greater Mark of Strength: Same as for quints. Reason I dont take Armor Pen is that E and W are Magic Damage. AD runes benefits all skills instead of going either Armor Pen(Benefits 1 skill) or Magic pen(Benefits 2 skills).

I only use this build in ranked.
Yorick is a great solo laner and really shines mid game if he has been solo laning.
But even if he is a great solo laner I always take the lane where I benefit the team most.
Example: If our team has a non-jungling tank like Cho'Gath, Singed etc. Then I'll let them solo top and I go Mid or Bot.

I can even Jungle if necessary (but Yorick jungler is not the best out there).
I prefer Mid Lane against AP carry (wich seems to work best for me).

This is how i play
For the first 0-20 minutes i play Yorick as a mage (building manamune and stacking up mana with Tear of the Godess).
Setting up harasses like this, I'll last hit a minon with my Q skill to get the passive, then I use E on the enemy champion I've decided to harass and follow up with W instantly.
When i harass I always cast W last to maximize the dmg output from my passive (Worth mentioning, I always try to keep max range when I harass at low lvl).

After about 25 minutes when i got Manamune, Boots and Spirit Visage I start to play abit more aggresive.

Earlygame: Keep distance and try to harass at maxrange. You are not tanky.

Midgame: Starting to deal good dmg with Manamune and Sorcers boots. You are a bit harder to kill cause of Spirit Visage and E skill.
Try to sneak by their CC and Unleash the slow on there carry and see if your team goes for it, if they do, activate Q and go for the kill.

Endgame: Now you are a beast and should be able to run straight in to the teamfight after your tank and aim for there carry, AD-range prefered. Since they will need to try kiting you and wont be able to autoattack during the fight and your burst will get her down to 50% instantly.
Ulti should either be saved for ressing a AP carry or casted on AD carry early in the teamfight for 6vs5 advantage. Remeber to set target for your Ulti.

Yorick is really effective killing AD-range in teamfights. Stick to them like glue with your Frozen Mallet, W and Q skill. They will hate you and your team will love you.

Farming is really easy with Yorick as you have Ghouls that auto attack dealing extra DPS, the Quints and Marks makes last hitting really easy and you have an AoE ability as well that helps you clear waves.

He is one of the best tower pushers in the game, pop ulti on yourself when hitting a tower and spam W and E,Q if any minons nearby to grant yourself your passive for increased dmg on towers.
Ghouls also attack turrets.
This is insanely effective endgame.

Pros:

- Good Laning Phase
- Awesome Sustainability
- Good burst early game
- Really Good dmg output endgame
- Tanky Endgame
- 2x AD carries with his ultimate

Cons:

- This is not a problem but worth mentioning, Yorick is kinda squishy the first levels.
But the heal from E is enough to compensate that.
- Can't really figure out any more cons, my build pretty much builds him strong for mid- and
endgame.