Please note that this is my first build.
The work of gravediggers is essential amongst the living, but invaluable in the Shadow Isles. There are many shades of death there, and each is embraced rather than feared or reviled. One can only ascend from one state to the next with the magical aid of a skilled professional. At the end of the first Rune War, Yorick Mori made his living as a gravedigger. His family owned and maintained the Final Rest Memorial, one of the oldest cemeteries in Valoran. The shovel he employed for his work had been passed down for generations. Each gravedigger taught his son that this shovel was imbued with the spirit of every forefather, and that those spirits would protect him during the long lonely nights amongst the tombstones. To his eternal regret, Yorick died without an heir, bringing the proud Mori line to a close. His body was interred with his shovel in the family mausoleum, and the Final Rest Memorial soon fell to ruin. Death, however, was not the end Yorick had expected.

Yorick emerged on the haunted shores of the Shadow Isles - not quite dead, definitely not alive - still clutching his beloved shovel. He soon learned that with it he could act as a ferryman for the Isles' undead denizens, helping them climb death's many-tiered ladder. This proved a curse, as a gravedigger must ''bury his quota'' before he too can ascend, or so the legend goes. No one knows what ''his quota'' is. Yorick dug tirelessly, waiting in vain for the day when he would be freed of his burden. As decades turned to centuries, the shame of his failures came to a head. He returned to Valoran to find his corpse, convinced that salvation might be buried with it. When he arrived, no trace remained of either the mausoleum or the memorial. Hope nearly lost, he discovered the League of Legends, and there saw an opportunity to immortalize the family name he allowed to be forgotten ages ago.

''Die first, then we'll talk.''
-Yorick

Pros

Abilities are named after the four horsemen (rather cool in my opinion)
A lot of health, at least the way I build him
His ultimate is pretty amazing if you can use it properly
Really cool skins (If you still haven't noticed his pentakill skin looks like slash)
games for me usually never last past 25 or 30 minutes (around the time I'm getting Warmog's)

Cons

Not much Armor or Magic Resist the way I build
You need a decent amount of minions or kills early game to do well
requires a decent amount of skill to play ( cant just buy him and do amazingly with him)

Yorick cannot farm well at all! he is terrible at farming at least I think so because all of his skills are single target except Omen of Pestilence which doesn't do enough damage. So if you can early game just focus on last hitting minions with your auto attack and trying to stay alive until you can get a kill.

My runes are pretty self explanatory I get armor pen. marks for early game when people have no armor so I'll do more damage. I get the seals of clarity because they're cheap and give nice mana regen per 5 which everyone knows Yorick's mana pool is pretty much non-existent. My blue runes and quints are for higher chances of survival early and late game.

The masteries are rather simple, 0/9/21 with more into mana regen so you can stay in lane longer but these are my choice you can go more defensive with your mastereies with 9/21/0 or 0/21/9, or more offensive with 21/0/9.

Ok well I start off with a Meki pendant and 2 potions it is your choice as to what potions or any at all (I highly recommend them) i get the mana potion just in case i run out of mana which you shouldn't do unless you spam your abilities before tear of the goddess. I get Mercury Treads after for the movement speed due to the fact that Yorick is amazingly slow. I get sheen after because it procs with your Omen of War i get Warmog's Armor after so i can be a better damage sponge i get Phage for Frozen Mallet after that for the bonus damage and slow/health this item is optional you could get a Banshees veil or or more defensive item depending on your preference. I then get Manamune because at this point in the game (assuming you even get this far into it) you should have enough mana for a nice amount of bonus damage from it. As for my last two items they should be self explanatory Trinity force for all the bonus stats (mana for Manamune health for the Atma's you will be getting soon the bonus damage proc for your Omen of War the AD/AS bonuses are nice to and the movement speed is very useful) I get Atma's for the bonus damage from all the health you should have by now.
And that explains all my item choices.

Ok now for my skill sequencing I max my Omen of Famine so you can stay in lane long enough to get your tear of the goddess and its really annoying to enemy champions if you use it right. I max Omen of War after that because that your main damaging spell. I don't max out my Omen of Pestilence until I'm forced to because the slow is nice but early game people usually destroy it as soon as you drop it I get the on point in it early game because the initial slow is nice and if used properly you can use it to block skill shots like Ezreal's Mystic Shot.

My summoner spells are my preference i know some people like flash or ignite or maybe even cleanse but for me teleport and ghost seem to work the best, though if you do choose other summoner spells I highly recommend flash and ignite flash is amazing for escaping and positioning and ignite is good for killing the people who get away from you with almost no health.

Yorick is a great damage dealing off tank and if his ult is used right he can help a team-mate get kills even after he or she dies but all in all hes a really good underused champion in my opinion. And please note this is my first build ever so please don't downvote it without a comment because if there is anything wrong with it i would like to know so i can improve it.