I hope She meant underrated but then the mentioned Lee Sin pick would defiantly mean overrated since he is picked very often.
Anyways, Yorick is UNDERRATED. He wins most lane match ups and his sustain is through the roof. He does tend to push his lane, so that can be a downside. The upside however is he doesn't give a flying fu*k. Most of the time you can safely farm solo top pushed to the tower because the enemy will be low and the enemy jungler won't be able to do anything about it. If the jungler ganks just W to slow him and Q a creep for extra movement speed.
Runes I use are MS-Quints AD-Red Armor-Yellow MR-Blue.
Mastery is 9/21/0
Ability order depends on the game but most of the time is R>E>Q>W picking up W first in order to check bushes, early slow, and the ability to level tear. If kitting is needed go with R>E>W>Q.
Item build I go with differs game by game. Tear first always.
Tear>Boots + Ruby Crystal
If you are winning lane by a large margin and do not see a threat from the jungler turn the Ruby Crystal into a Phage. If you are even and or see the jungler as a threat build it into a Spirit Visage.
If you went the phage route continue on with a Tri Force then Spirit Visage and Omen's after that. Manamune thrown in whenever you feel like you need the extra damage.
If you went Visage get a Giant's belt after. Then work towards your Tri force and finish Omen's after. Manamune thrown in whenever you feel like you need the extra damage.
The rest depends on if you need to get more tanky or more damage so build accordingly. This is how I build him.