This is my build for Master Yi. I think this is the most effective build. with this build Master Yi has huge damage, attack speed, critical damage and life steal. Enjoy!!!

I chose this runes because you need attack speed and critical chance.
You can also use some movement speed but i thin this is better.

For masteries you just pick the offence because it's very offensive build!

Stark's fervor will give you attack speed, critical chance and damage, it's better than Phantom dancer at begin.
first you buy 2 BF swords because you need damage, if you don't have gold you can buy first The Black Cleaver.
After 2 BF swords you can buy the black cleaver and after that the Bloodthirster.
then you feed bloodthirster with 40 minions and then buy infinity edge.
this is enough to become KILLING MACHINE but with phantom dancer you'll be real MASTER!!! enjoy

use alpha strike to kill minions and earn some gold.
combine wuju style and highlander to kill enemy fast!!!xD

exhaust and ignite is good combination.
except ignite you can buy flash to catch them all xD !!!

i hope you'll like my build!!! do some pentakill for me xD