This build is for AD Master Yi. I think this is the best way to play with Yi because your normal hit makes your enemies very angry. Also when go AP you just have one ability which is Alpha Strike. This is my first guide, so let' get started.

For starters, you should get armor pentration because it's important to get first blood.
Secondly, get Armor because I don't purchase armor items during the gameplay.(Although sometimes Guardian Angel may be needed if it gets too hard to keep up)
Thirdly, get Cooldowns for Yi's Ultimate.(Use your Ulti and take one kill, then you can use your Ulti. If you use your Ulti again and assist someone next cooldown will be 16 seconds. You can get one more enemy after that 16 seconds.)

21, 2 and 7. Why ?
21 for first blood and early game.(Critical Strike is very important when playing with Master Yi)
2 because you don't wanna die while you are trying to get first blood. (If your teammates are noobs and not premade, this can be quite annoying)
7 because you need mana and mana regen. There is no mana buff on 3 vs 3 so these are very good for you.

What You Should Get

Flash: You will see how much you need this spell in early game.
Exhaust: For stealth Champions. Use it against them to run away from them or to kill them.

What You Shouldn't Get

Ignite: You're not a AP Champion so you may not need it if one of your teammates already have it. If you see a good healer enemy Champion you should probably get Executioner's Calling.

Try to get first blood but don't push so hard.
Go up.
Kill minions using Alpha Strike (You'll farm easily) to get Level 6. When you are Level 6 if no one got First Blood yet look for enemy champions without stun and try to kill them.
If your teammates are noobs and don't 'ss' then you'll get killed because of your teammates.
I propose premade teams because everybody will try to kill you if you get first blood and Avarice Blade.
You must get Long Sword to do more damage.
At this point you will have both critic and attack damage but the health points will be a problem so you need to get a Vampiric Scepter and another Long Sword because life steal is very important. When you have 2x Long Sword turn them into the Brutalizer.
Take Youmuu's Ghostblade and go for the dragon.

While you are fighting with the dragon use your ultimate (i'm not kidding) because you must be fast and go down to help your teammates.
If you are premade your teammates may call for help.
Help your teammates and go for the first tower in the top section. After you take that tower go back to your base(don't forget to activate Youmuu's Ghostblade).
If you think you're getting too much damage then take Ruby Crystal and turn it to a Kindlegem.
Then take another dagger (Your can't use your passive because Yi won't be quick enough).
Turn all this items into a Zekes Herald.

Now it's time to finish the game.
Go up for thwe dragon and push the minions a little bit then turn to the base.
Go down with your teammates and take the first tower (if your teammates still didn't )then go for the second tower.
If you see just one enemy, cover the tower than go and attack it (with teammates and minions of course). If you see two enemies cover the second tower than attack the one with low health and go for a kill. If he uses flash then go back to kill the second enemy. If he starts to run go a little bit back to and destroye the tower with your teammates.
After the second tower go back to your base.
Take guardian angel if you take so much damage.
Take infinity if you want to kill enemies quickly (take it if you have a premade team)
If you have premade teammates then tell them to cover you and attack the final tower. Your damage to the tower must be 120 so you will destroye the tower quickly.
When they only have Nexus left go for a sneak attack.
At the forest path behind Nexus use your flash to Nexus and use your ultimate and Wuju Style ability and of course your Yousmuu's ghostblade.(Tell your friends to attack and you will smash them like Hulk :)
GG you win the game.

Doran's for first blood.
If you think you can get first blood without Doran's then you take 2 health potions and boots of speed.
After the first blood get a boots of speed or dagger if you started with boots of speed.
Then farm with your Alpha Strike and complete your Berserker's reaves and get Brawler's gloves for criticals.
Turn your Brawler's gloves to Avarice blade and get more criticals.
Why are criticals important?
Because you get attack damage wih this Wuju Style ability.
Take Long sword to get more damege and right now you must have 100 or 120 attack power.
But you don't have a Life steal item so when you take Vampiric Scepter you're going to like that 'Double kill ,Triple kill's. Now what we want to complete is Youmuu's Ghostblade so take The brutalizer and complete Youmuu's.
You must complete the Vampiric Scepter to Zekes Herald but if you have too many kills you can also complete that to a Bloodthirster.
After you got Bloodthirster take a Guardian angel.
If you get Zekes Herald then take an Infinity Edge or if you take too much damage then take a Guardian angel. If the game still continiues then take an Infinity Edge.

In this photo i got 6 kills without dying. Then went for mid and got triple kill between two towers. Why did i play with Gp in between? I really don't know.