Yorick is not the easiest champ to play but, you will have a lot of fun and good results if you use it correctly.
This is only a itemisation, because the champion is to new to make a full guide but i will add more chapters andthe guide of the correct form to use it soon.

The most important part of Yorick are his ghosts so, the build is focused in making them and therefore himself, the most powerful possible.
The ghosts benefit from your health and your damage so you must use yor gold to improve this features and there is no better awy to do it than building this items.
Trinity is the best item for offtanks and tanky DPS so, i think hat i dont have to explain how it works.
I know this items are not the cheapest, but try them, you will notice that they are the best option.