Yorick is slow. And being slow you want to make sure that you can either come back to lane with no problems, or you want to get back to lane NOW. I always take teleport with him. It also gives you the ability to gank with him if you see that your bot lane is pushed hard to the tower with a ward behind the enemy to come in and either give some relief or pick up a kill. It also allows you to join a team fight late, and still make a difference.

Damage is not a problem, but sometimes you just need to make sure that you get that kill, which is why Ignite should be there.

Other summoner spells to consider:
exhaust for extra slow down and armor reduction to get a kill
cleanse if you are going to go against someone that can dot you a lot.
Promote to get extra push and tower killing power.
Flash if you want to jump and follow to get a kill.

Ones that I would avoid:
clarity-you wont need this at all after you get frozen mallet
clairvoyance-support should take it more.
surge-his only AP ghoul wouldn't benefit from it much.
ghost- you have a slow down ghoul, so them getting away shouldn't be a problem, if it is, get frozen mallet for extra damage and that extra utility.

I have changed the masteries on this build to give me more gold in top lane when I get a kill or assist. I have found that even with this minor change I can get fed more quickly and out pace to the items that I need to be basically invulnerable.

The also give me sustain in lane by adding in the MR, Armor and health. You can sap a point from the utility tree to add in to defense and it doesn't hurt.

I have found for runes that making sure that you get damage for early game with the Marks of Strength is the best way to go. This gives you early life steal advantage, as well as beef if you get in a knock down drag out early.

For defensive runes I only run just the few MR per level glyphs, but if you wanted to sub out and go all 9 I don't think that it would hurt your performance any. I don't run them now because I find that Yorick is mana hungry and the extra mana regen per level glyphs keeps me in lane a lot longer than most. I do run 9 armor seals which gives me pretty good damage mitigation early.

For quints I run 3 flat damage. Again it is for early game crush, and late game bruise.

For early game sustain you really want to make sure that you have as much life steal as possible. This also gives you harass. Stick with making the E (Omen of Famine) by level 9. In between leveling that you want to also get utility with slowing them down (Omen of Pestilence) maxed by level 13 and then movement speed with Omen of War last. As always you want to max your Ult at 6/11/16. You can use Omen of Death early game to dive towers and pick up kills. You can also use it to take down towers even if you are going to die while diving by stopping and just hitting the tower, and then when you come back as your shade continue to hit the tower.

The best damage burst combo for Yorick is to thrown down W/E. This slows them down and starts dealing damage to them and giving you life back. If you happened to be in range to melee them, the q/w/e and watch them hurt. This combo works best around levels 7 and 8 fleshing out after both Pestilence and Famine are maxed out.

Yorick can be very easy to CS with. Its tempting to smash them all the time with ghouls that provides you with free harass, which is something to consider, but it drains your mana very fast. Early game (before manamune) take it slow with that and only really use the Omen of Pestilence to harass with as that keeps you in lane. If they keep trying to bully you, bust tou the w/e combo on then and they usually run away.

As you build up in items you will find it easier to farm with and it makes it more comfortable to know that after Frozen Heart and Banshees veil you are really hard to take down.

For Yorick I have found that the items are really flexible. But for this build you want to focus on getting items that are going to feed you protection and damage.

Core Items:
Getting early Manamune gives you damage which builds into sustain for the life steal ghoul. Rush that. Then move to frozen heart and follow quickly with banshees veil.

Flexible items:
Staying with more damage mitigation and sustain is key. If you have the time for it, build Maw. That will give you more damage, and make your ghouls beefier as you die, which can help sustain you. If you need the move speed get the FoN that is on this build. If you get Maw, also build the mallet that way you have the life to feed it, but the mallet is not necessary. Spirit Visage can be useful but I really find that the extra life regen that you get from it is better off of the FoN.

Boots:
Most of the time I got for merc treads, however you want to build what is going to benefit you more long term. If they have a lot of AD get ninja.