Yorick, the Gravedigger
This guide assumes you will be in the solo lane as Yorick, for that is where he really shines. He makes a rather poor lane partner, and is sub-par in team fights till the mid game anyways. While support Yorick can be done quite well, it is very very different from this build, and generally there are other champs that do that job better.
One of the largest misconceptions about Yorick is that the role he fills is a simple one of either the tank or the bruiser. This misunderstanding is what often leads to failure with him. Yorick has some of the lowest starting base health and defensive stats in the game, in the beginning you are very squishy and are not a close range character. His role changes over the game, you start as a ranged caster, and then you shift into a bruiser state around the time you get frozen mallet, and then finally a high damage tank towards the end of the build. Understanding that you do not start the game as a herp derp close range right click to win character is vital to succeeding with yorick. Also note this build is largely designed for 3v3, while it will still work fantastically on other maps, the runes and masteries would be set up a bit different for 5v5, and the items would be a bit different on all the maps.
The New TT
So the new twisted treeline had been a drastic change, but the map has been an overall buff to Yorick. Thankfully there is a built in mana boost on the map with the alters, this completely removes the need for potions at all on this map, especially with the increased gold and decrease in the cost of tear allowing you to buy it strait out.
The map its self is pretty strait-forward, capture alters, jungle if your lane is to far pushed. Wreck the top lane with yorick. Be careful only to last hit and not push your lane, unless the bottom lane is equally pushed back so you know a gank wont happen. Ganks on this map happen faster, and more frequent then living in the top lane on 5v5 with a very ganky jungler. Map awareness does not cut it on this map. Your team has to call mia, and you need to do so as well. Even if you are 100% sure that person is still just standing in that bush right there, you need to call it. On 5v5 getting an mia is a courtesy, here it is a necessity, for the time it takes to go between lanes is mere seconds.
Remember yorick is not a strong ganker until after your frozen mallet, so try to encourage a long laning phase, and before that health-boost from mallet he gets bursted down really early, so its best to avoid committed team fights until then regardless. Also ask that your team just pushes their lane, rather then trying to gank yours. Once the ganking starts, the laning phase fades out pretty quickly, yorick lives for the laning phase. So you want to do everything you can to encourage it. While ganks may yield good results, they are also risky, its better to just encourage the laning phase by keeping people to busy to gank.
On alter control, just try to maintain your own, don't try to steal the opponents unless you are sure its safe, meaning you just won a team fight, and most or all of their team is dead.
On Vilemaw (I comonly refer to him as spiderman, he was the replacement for dragon). I can not stress this enough do not take him unless you are 100% sure its safe. Also his power rivals that of barron, and he has massive aoe damage, and a stacking dot. Yorick can take him earlier then most people since spiderman will waste attacks on the ghouls saving your team from that deadly stacking dot. However even with yorick, blowing your ult and everything, the earliest safe time to take him with your entire team is about level 15 assuming its an average game and you and your team isnt far behind. If you are killing him, make sure you and your team stand on opposite sides of him that way his aoe is only hitting half of you at a time. Many games go bye without vilemaw ever going down, and that is just fine. He is horribly high risk and high reward.
So your the bruiser, but whether there is an ap tank, or a mage, and their better be one of these on your team, beg them to buy Banner of Command and do so fast, not only is it a beautiful item that has great stats, and really helps bottom lane push, it also increases yoricks power exponentially since each of his individual ghouls gain its benefits granting a massive damage boost.
Have a balanced team, and remind your team of the TT specific items because they are really op. watch for ganks, be passive with spiderman and alters, discourage ganking, and you should preform very well.
Ignite is the obvious choice when it is your job to kill people, I choose ghost over flash because it is more useful for kiting and chasing, and with the new changes to the twisted treeline there are few walls to flash over anymore anyways.
Flat AD runes are what Yorick needs. By the time your level 18 the amount of damage you gain from levling runes is quite pitiful, what really matters is you geting a few kills in the early game, and considering everything he has scales off of AD this is how you do it. It makes his ghouls hit hard, it helps him last hit, and makes his own attacks effective. Also while most people use armor pen runes, they are bad on him, because his ghouls only scale with ad and not armor pen (Actually riot admitted despite it not being on the tool-tip they do get armor pen, but they scale much better with ad). Those movement quints are a must! First off, I put off boots until after Manamune this helps here. Secondly, since I'm not building any other speed items this helps here. It makes Yorick into one of the best kiters in the game, as he runs he drops ghouls behind him. Not to mention will help immensely in chasing people down for those early kills, which is what the whole focus here is. While magic resist and armor are other popular picks to help with survivability, more AD means more life-steal with your red ghoul which inevitably tends to lead to better or at least similar survivability to having those defensive runes. And unlike the 5v5 map there is a lot less burst damage coming in so lifesteal and strait health tend to mitigate smaller amounts better than resistances.
My main reason for using the utility and and offense trees is the cooldown in both. Yorick has fairly short cooldowns as is, but he doesn't have much room for cooldown items, this helps with the ghoul spamming which is what makes Yorick tick. The extra ghoul or two you get to put out from using both trees will be more damage than going through with the pure offense tree. Also, the movement speed buff is another must for the kiting and chasing. Remember, you have Manamune so geting extra hard mana is more AD, not to mention helps with his early game mana problem.
is perhaps the best mastery in game, so that is an obvious choice. And hey, if you use the summoner spells you should have the mastery for them. Oh and on spellvamp, his red ghoul and green ghoul do magic damage (Despite red scaling with ad) so it works on both of them to great effect. (They also work with life-steal)
Yorick's mess of skills are ridiculously complicated in the way they function, to understand him you must first understand the weird mechanics behind him. The first point is despite that his ghouls deal magic damage they scale off of AD (except Omen of Pestilencewhich scales with ap, but its attacks still scale with ad). So more AD means more damage, both magic and physical. So that small part aside we come to his passive. Oh boy it is long. But to break it down, ghouls get 35% of his health and damage when they make there own auto atks. And to top this off for every ghoul he has out, including his ultimate, that is a 5% damage increase, and damage reduction. So with all 4 skills active that is a 20% damage boost, and 20% damage reduced to him, and keeping the ghouls around requires more health.
Omen of War is your primary damage skill, and boy does it hit hard, not to mention making a very fast ghoul it makes Yorick insanely fast. So other than when you're bashing someone's face in with it, it has two other uses: either hit a minon with it to give you a large speed increase to either chase someone down or run away. If your geting ganked and you have at least a quarter of your health don't be afraid to turn around and whack the nearest guy for the large movement buff. Also if you time it properly and use it right after an atk, it resets his atk timer for a second atk.
Omen of Pestilence has a huge amount of utility. It should always be used to start your combo, drop it on the opponent before you use your e and rush in with your q. This also makes him a fabulous kiter drop it behind him as you run. Another unique use of it, beside the obvious bush check, you can drop it over walls to get vision, this helps prevent ganks, it also is treated as a minion so it blocks skill shots, and can pop Shaco boxes and Teemo shrooms. Generally you use this and your E for harassing, you sit there happily farming minions ignoring your opponent, until they get foolish enough to either try to farm minions themselves or try to attack you. As soon as they do, hit them with this and your e, and go back to what your doing. A few of these will drop them down to half health, about that time when you get to drop this and your e again, its time to chase them down because you will easily be able to kill them now. However note, you are not fantastic at strait melee early on, so you want to make sure to harass them down before you commit to melee.
Omen of Famine is his bread and butter, it's his primary ranged damage, and it gives insane life steal, use it to refill your health on minions or do very good damage to your opponent. Always level this first, it has amazing damage, perhaps not as much as your q, but the range on it makes it better. And of course it has the nice combo with w as I explained.
Omen of Death is his awesome and somewhat complicated ulti. I suggest always explaining how the damn thing works to your team, I get so sick of popping it on someone because they're about to die ...only to watch them run away and waste it because they think I'm Zilean. My main use of it however is pushing down buildings, not only is the extra damage nice, but you can aggro the tower with it. Yorick doesn't need minions to push a tower, towers will choose his ulti and his ghouls over him. In team fights always use it, and against a melee opponent it makes 2v1, not nearly as good on a ranged champ, but if you're in their face the extra damage it will do is nice. Now to explain how it works. It makes a clone of an allied champion (usually yourself) that makes auto attacks, you can control it with alt like most pets, if the person its cloning dies while its still going, it disappears and they come back at full health and mana for the remainder of the duration, and then they die again. As this is a high AD build you are the general target for it when you want the clone, but don't forget to use it if someone who is useful is about to die.
Note Maw of Malmortius and Hexdrinker are not part of the core build, you only build them as a replacement for frozen heart on the off chance the apposing team is primarily AP. (Allthough while Vandamns is disabled, it has become part of the core build) Mercurial Scimitar is a good alternative to maw if they have a heavy CC team, I usually prefer maw primarily due to the fact that Actives can be difficult to remember in really quick and brutal situations.
Understanding the way his passive synergies with his skills it is absolutly essential to understanding him. More AD means more damage the ghouls deal with there summon and there auto attacks. More health means they stick around longer which means more attacks on top of there awesome effects. So sure maybe having atk speed and crit would make me hit harder, but were not talking about me with Yorick, we are talking about WE, every second more those ghouls stick around is another few attacks, not to mention his passive when you have all 4 abilities active gives him a 20% DAMAGE INCREASE, on top of the 20% dmg reduction. AD is the only offensive stat that you care about as Yorick, nothing else scales with his ghouls which are his primary source of damage. Also health is the only stat that carries over to them, and them sticking around longer relies on that. Thus why Frozen Mallet is such an essential core item. Building him this way not only makes his survivability shoot through the roof, it makes him hit stupid hard.
To summarize Trinity Force is a popular item on him, but it is a complete waste of money due to the number of stats it has that don't scale with his kit at all, that is usually why a Yorick is sub par at best. If you waste your money on trinity for Yorick, I am sorry, but you are just bad.