Hello and Welcome to my first Mobafire Build . This Build is about having some fun with Master Yi . I would really like to see some comments and if you can , give some Criticism so I can improve this Build here to help you playing Master Yi succesfully .

For Summoner Spells I take Flash and Exhaust but also good Choices would be:
Ignite
Ghost
Heal
Cleanse
Smite
No - Go's:
Clairvoyance
Clarity
Fortify
Rally
Revive

Core
Infinity Edge
Black Cleaver
Phantom Dancer
Bloodthirster

Optional Items
Sword of the Divine
Wit's End
Youmuu's Ghostblade
Stark's Fevor

After the Game started , grab Brawler's Gloves and 2x Health Potion and go up in your Lane. Try to stay in Lane till you farmed 1200 Gold to grab up Zeal and Boots.
Then go on farming till you can buy your Berserker's Greaves and your first B. F. Sword.
Go farming again and complete your Infinity Edge.
Now in Mid Game you should have gotten some Kills and be able to complete your first Phantom Dancer.
Then after about 30 Minutes in the Game now buy your Black Cleaver and start getting another Zeal to complete your second Phantom Dancer. Then I usually get a Bloodthirster for the Lifesteal and the Damage it gives to you.

As Master Yi , you can take out their Carry easily and then you just destroy the enemy Team from behind. But it's important that you don't overextend and that you aren't too greedy.
One Tipp I got for you playing Yi in Teamfights. Don't initiate!
Let the Tanks or Casters initiate so the Carry doesn't focus you and you can take the Carry down fast and then rape the others from behind.
They will be like "Woah , Wtf happened?"

Have fun playing Yi and don't be afraid to leave a comment under this Build.
Thanks for reading my Guide ,
NuclearScan