I have been playing LoL for some time now (almost since it was released) and along my experience in the game i discovered that the buying order of items can be helpfull, and sometimes determinant. Start with Meki pendant and 2 Health Potions , try to farm as much as possible until you have 680 gold (DO NOT PUSH THE LANE, Try to last hit with auto-attacks) after that you can push a little so you can recall and buy and when you get to your lane you wont be losing farm to the tower. Ward your lane asap, and now you can farm with an extra security, keep farming until you have enough for Long Sword and Ruby Crystal, and of course another ward ( if you dont have enough money for both items and the ward, just buy one of them and a ward, wards can save lives and win games always remember that). By this point you should already have some assists or even a kill, if you do perfect, you will dominate your lane even more efficiently, if you dont that's ok, either way, stick to the plan and continue with your farming until you can complete your Phage and buy the Chain Vest and possibly even the Null-Magic Mantle for your Mercs. At this point the only thing left for you to do is to complete those Mercury Treads and your Glacial Shroud. That will be your core build after that, you just need to finish your Manamune and your Frozen Mallet obviously, and the rest of the items can be situational altough i recommend using Banshees and Atmas Impaler. Why you ask? Like i said this is a balanced build and for me the most effective on Yorick. You can Tank and deal damage. With banshees added to the build you will have around 3k hp and 3k mana (Plus some extra Magic result and a nice passive as bonus) and since your manamune gives you AD based on your Maximum mana you will profit from it, adding Atmas Impaler to the mix Increases your AD (based on your Maximum HP) even further and gives you some more Armor and a little crit chance.
Conclusion: Manamune will profit from banshees and your defensive stats will increase.
Atmas will profit from the extra hp of banshees and also add defensive stats.
Important Note: Only complete your Manamune AFTER you get your Glacial Shroud, because before that, the waste of about 1000 gold will not be worth it.