With the right masteries and runes(the way i use them), combined with ionian boots and glacial shroud, gets me at 39.89% cdr. Ghoulspam incoming.
My cookiecutter build for SR: Manamune, Ionian boots, these 2 are first. Unless there is a reason i can't finish them because of...(insert reason).
From there on early glacial. Frozen heart very late. The mana increases by 75, the cdr increases me over the limit. The item is too expensive for the stats it would give me, so leaving it there for a long while.
Then, the other items are FoN and Triforce. Now i'm running around with 474 ms, and >530 when Q'd. As long as there is something to whack, only the double PD people are able to catch up. Sheen can be built early, but if you're having a hard time with magic harass, get that negatron first.
6th item is situational.
As yorick it's important to zone the enemy as early as possible, but NEVER push the lane. This is actually quite hard as W and E can target minions by accident pushing the lane. If you push too hard and the enemy is under the turret you are actually in a bad situation. Yorick's minions will chase an enemy, and guess who gets turret agro for that? Yorick. So yorick can't towerdive properly, unless he's planning on losing a lot of health.
Bottomline, don't push, zone agressive. Push when you have the advantage and a few stacks on manamune/tear so you can let the ghouls do the harass under the turret. (as long as they do, you can't approach turret safely)