Im a OTP mordekaiser player who made a smurf account only to play Yorick. After getting to diamond with him, i think i understand most parts of the champion. I dont think i have reached a completetely pro level with him like i did with morde, but anyway i wanted to make a guide.

Yorick is such a special champion, my favourite along with Mordekaiser.
There are some things to comment about him:
-Hes currently considered a weak top laner, and this is right. He is playable and has good things, but if you are looking for a broken champion to scale leagues, this is not your guide. Play this champion for fun or if you like necromancer magic and ***** like me.
-His strongest point is maybe his counterpick; inmovile champions who hasnt a very strong 1vs1 potential are extemely weak aganist a good yorick, its like picking an assasin aganist an adc.
-...But, if you are in a unconfortable matchup, the game can be a real hell. There are some champions in the game that you should never face being yorick.
If you like necromancy and shovels, lets begin.

Most people gets HP per level, MR, damage and some armor and even some of them get CDR runes. In my opinion this is not really necesary, specially the CDR part.
My yorick runes are pretty simple: 9 armor, 9 Mr, 9 attack damage and 3 quints of damage.
The reason? well, yorick has a good stadistics by himself, 30 armor at lvl 1 and 2400 HP at lvl 18 (and 142 dmg at 18, the 3th best in the game) are not bad at all.
Yoricks Q heals based into a flat number, so it is better to have more resistances and less HP. I know this logic could not sound convincent, but it worked pretty well with me. Do what you consider good.

You have 3 options here; warlords, stormraiders or garsp.
Warlords gives a good sustain and agility, garsp makes you stronger in close fights and stormraiders is oriented to snowball and move on aganist squishy champions. Its usually said by the most experienced yorick players that stormraiders is the best, but all of them are good (in my case i preffer garsp). Play some games with each one and choose wich you like more.

Well, heres where the things get serious: The build i use in almost all my games has 2 variations, and some situational minor changes. The start is always the same;
begin with Corrupting Potion, after the first back build Phage or its components if not enough money. In the second back, get upgraded boots, tabi aganist heavy AD and mercury aganist tanks with heavy CC or aganist mages. In the third back get Sheen, and after this go to lane and try to not come back until you got 1400 gold, so you can get Trinity Force. when you get this items, the next one must be a tank item wich should be one of the nexts: Dead Man's Plate, Randuin's Omen, Spirit Visage or Adaptive Helm. The option you get depends on enemy team. Get only one of this items for now.
After this is when the build gets changed depending the game;
if you are in snowball or at least doing good, then rush Death's Dance. This item is fantastic with yorick, It will give a lot of damage to your ghouls and your Q, and along with Elixir of Wrath will make you nearly invencible in 1v1 duels thanks to the healing.
Then get the other tank item wich you didnt get before, you can get 2 items of armor if the enemy team is full ad or even get Thornmail, but the most optimal option is get one of the mr items and other of armor, so you get a lot of hp, good resistances and 40% cdr.
As last item, get Sterak's Gage and always and active elixir.
If things gone wrong and after building the first tank item you are behind, or there are much champions in the other team who counter yorick in 1v1, then you can use this secondary option:
as 4 item (counting boots) get Banner of Command. This item will give you good resistances, 10% cdr and its extremely cheap so you will compensate the gold difference with the other champions in the game.
after that do the same of the first option; other tank item and sterak.
tips:
after getting Death's Dance, procure having always a Elixir of Wrath (you can carry it in inventoy and use it when needed). Try to always have it active when going 1v1 anyone. You can dive most champions if they are alone.
To use Banner of Command, go to a lane wich is pushed to your side, kill 4 minions using your Q but do not raise the ghouls yet. Wait until a cannon minion comes from your side. In that moment, use banner with the cannon, raise the ghouls and let them attack at least once to enemy minions, so they enter in "pushing mode". When you do this, that wave will destroy everything in its way until an enemy champion comes to stop it. If the reach an enemy tower, the empowered cannon minion will tank it and deal a lot of damage while your ghouls, safe from the tower aggro, literally eats the tower and causes masive damage. Before the cannon minion gets killed at least one enemy tower will fall. This is great because you are creating a distraction without even being present in the place, so an enemy will have to go that lane to clean it and you will be able to seize that to get objetives or force a 5v4 and peel for your team. Try to give pressure into an objetive or tower at the same time your empowered wave is approaching the enemy tower in other lane.
Situational items:
Randuin's Omen- in the case there are much critic champs in the other team. Get this instead deadmansplate.
Adaptive Helm- in case there are much champions based in continous ability damage (cassiopeia, mordekaiser...), get this instead spirit visage.
Thornmail- aganist AA and heal based champions.
Zz'Rot Portal- NEVER build this. Good resistances but most useless active in the game.
Black Cleaver/ Iceborn Gauntlet- considered an alternative option to trinity, i dont recommed it really.
Titanic Hydra- not a bad item, but not as usefull as others and expensive. I dont recommend.
Gargoyle Stoneplate- not recommended, with banner and 2 tank items we have already enough resistances. the active is useless as hell into a juggernaut, even if you are going to peel, your damage must be there.

Yorick is an extremely funny champion, one of the best desinged ones in LoL and a great option in top lane once you get used to him, but its not as strong as others (i still thinking he needs some mini buffs)
Get fun by smashing people heads with a shovel while your ghouls laugh at them.