Yorick is a really good solo champion (not mid), he is usually going top cause that's were the tanks/off-tanks goes.

Its good to go with a long-range character because you want the advantage of the lane which is best with one short range and one long range, and because Yorick is a short range with long-range abilities (if you don't count he's Omen of war and Omen of death) he is allowed to harass the opponents with minions.

Omen of war; is a short range attack that deals 30/60/90/120/150 +120% of your attack-damage to the enemy.
it summons a ghoul which deals 8/16/24/32/40 + 35% of your attack-damage, while the ghoul is active, you gain 15/20/25/30/35% bonus speed, which is good for escaping and chasing.

Omen of pestilence; is a long range attack that deals 60/95/130/165/200 +200% of your ability-power.
it summons a ghoul which slows your targeted area by 20/25/30/35/40% when it is activated and while it is alive chasing it slows for 10/12,5/15/17,5/20% in a small area, which is good for escaping and chasing.

Omen of famine; is a long range attack which deals 55/85/115/145/175 +100% of your attack-damage and heals for 40% of that damage.
it summons a ghoul which heals you for 100% of the ghouls damage on champions and 50% on minions, the damage of the ghoul is something I don't know, I will try to find it out but it might take a while.

Omen of death; is Yorick's ultimate ability which makes a undead copy of a champion in your team or yourself, use it wisely in teamfights, its good to use it on the one with most damage, but you should say that you ult them before the fight if they are not ready on it (most players stop concentrating on the game when they die, so its smart to say "I ult you in the teamfight if you die" or something like that before the fight) but if you are the one with most damage and wants the kills on your own, use your ult on yourself, cause you wont get the kills if you use it on your teammates, they will get the kill and you get assists.

When you have manamune you can farm with your abilities, its really easy because of all the mana you have, manamune is a most on Yorick so dont change it, it prevents you from getting oom (out of mana) fast.

If you don't have a manamune yet and you are going with a carry or with a minion-killing idiot tank (hello alistar), you will have to try to get the minion-kills they wont get, otherwise its smart to change lane with a support or a carry.

Mercury Threads; Gives speed, magic-resist and tenacity which is good against champions with much CC such as Fiora and Riven.

Manamune; Gives much mana, attack-damage and manareg which is really good for you, your basic attacks refunds you 1 mana if you haven't stacked it up already.

Trinityforce; Gives you practically everything, and because Yorick is a pusher, the passive of trinity which makes you deal 150% of your damage as bonus damage is really good with your Omen of war. It slows which is good for chasing, and sometimes fleeing.

Warmog's armor; give's loads of health and healthreg, nothing more to say, makes you less squishy.

Atma's impaler; Give's you critchance and armor, stacks good with warmog's armor so it will give you alot of ad (around 46 - 48 damage).

Hextech gunblade; gives you attack-damage and ability-power, lifesteal and spellvamp, which stacks with your abilities really fine-tastic :-)
makes your Omen of famine give you 60% health of the damage taken instead of 40% and all the other attacks will heal you too.