Hey so this is my tanky support Yorick build.
I take Armour and magic resist runes for a lot of survivability early-game. They really do help me a ton and will help you. And even late game after you have your full item build you will be very well off.
I like to build in the Defense Tree first for more survivability. Then I bounce over to the Utility Tree for mana regen which does come in handy.
I start off With a Meki Pendant and 2 health Potions because in the early game your going to want to harass quite a bit and let the enemy know that your there. I then wait to get Manamune because of the passive. It also helps because it allows for you to have more mana. I then get Boots Of Swiftness because Yorick is relatively slow. You could also take Mercury's Treads. I then get Phage for the extra health and a small amount of damage. From there I will buy Frozen Mallet. At this point your very strong and shouldn't be dying. I then take Spirit Visage for the extra magic resist. You can also take armor or damage. It all depends who your playing with. I then take Brutalizer and Youmuu's Ghostblade. The Active on Ghostblade helps alot and can be used quite a bit. I then top it all off with Guardian angel. As i previously said you can take more damage if you need.
I always take Omen of Pestilence the most because of the slow, it also does a fair bit of damage. I like to max that out as soon as possible. I then take Omen of Famine because of the lifesteal. Your enemy's should be harassing you at this point and its always nice to have lifesteal to regain your health. I then take Omen of War strictly because I like to summon 3 ghouls in team fights. And also because if your chasing you can always be sure that you will finish them off with this ability. I take my ultimate at every point that I can. Make sure you place your ultimate of important people and not just feeders.
I take Flash because I know I can always escape with it.
I take Ignite because I play against a lot of Vladimir's and Warwicks so it is nice to enter with when playing against them.
Anyways, thanks for reading my Yorick Tanky-Support build. I hope you have a good time with it. thanks