In this build i start off getting my first actual upgrade as Boots of Mobility because as Master Yi you will be very squishy at the start so you will need to run until you have your ultimate or you are high enough level that the boots don't matter. I suggest keeping them tell you need Trinity Force just in case, When you need your Trinity Force you will want to sell Boots of Mobility because you wont have enough room in your inventory to get Trinity Force. Trinity Force brings your Critical Strike to 100% and your AP to 100 your Critical is the main part of this build because with it you can run straight threw people and with your speed boost and exhaust they cant get away.The AP helps because you will need to use meditate every once and a while and the AP makes it heal you a lot more.The reason I have the life steal in this build is because well everyone knows Master Yi is squishy and the life steal makes it so you can have a face to face a lot easier. It also lets you solo Everything up to dragon in the jungle I'm sure you could solo baron if you really went out of your way to and got a lot of potions but I haven't been successful killing him without going out of my way.