Master Yi is one of those champions, that if used correctly can completely and utterly dominate the playing field. This is the way i play him in all of the games that i have played, perfected over the coarse of over 100 games.

feel free to experiment, but if you wish to turn Yi into a rapist, then you will choose either attack speed runes, or critical damage runes, however, as yi's ulti boosts attack speed massively, i build flat critical damage.

Items for Master Yi can differ from time to time to time, but mainly what you will focus is critical strike, damage, attack speed and movement speed. to start the game off, i like movement speed, so i buy boots to start, accompanied with health potions and a single mana potion.

mid game, it is important to have lifesteal and attack speed, so that you can maintain order in your lane.

end game, if you are finding it hard to get in kills (hardly ever happens with yi unless stunned, binded, etc.), than you are probably wanting to slow your enemy down, giving you more chance to slaughter them before they get away. this can be achieved by buying a frozen mallet, which slows opponents movement speed dramatically. also, it is important to remember critical strike = extra damage. with my setup, every hit should be hitting close to 300% of your normal damage, which should be around 350. utilising this 85% critical rating, 75% lifesteal, 1k base damage per hit and above two hits per second, it is possible to take down an entire team by yourself!

Alpha strike should always be used to either harass the enemy by using it on a minion infront of them, or as a fight initiator. once you are in the fight, it is important to activate Wuju Style, giving you an extra boost of damage, and giving you the ability to over power your enemies early game.
Master Yi's Ultimate move, is incredibly handy in all fights, as if you get a kill, it resets all your abilities cooldowns, meaning that as soon as you get one kill, and there may be a coward scared ****less of your awesomeness running, you can pounce on that ***** with alpha strike, and dominate another champion.
it is always important to play Master Yi agressively, and Never touching Meditate, as it drains precious mana, and when you build Yi you can just use you're lifesteal on minions or monsters.
MAKE SURE TO USE CLEANSE! most of the time with Yi, when you are built the only way you die, is when some ****** thinks "lets stun this ****er" it might not be a long duration for stun, but without master yi's attacks, he is very easy to kill. cleanse makes sure that if you get stunned, suppressed, and others, that you will continue to fight, and dominate.

in situations where you find yourself vsing other high damage output melee characters, dont be afraid to exhaust them. armor loss, damage reduction and movement speed reduction ensures that you will almost always be the victor.

pros:
complete domination of most champions, and almost guaranteed win.
cons:
Master Yi's ulti eliminates all speed reductions, however it does leave him open for stuns, snares, binds, suppressions, and alike, when cleanse is not up.

if you have any questions about my build, how to play him, any suggestions, or want me to add more to this, dont hesitate to post below, and ill get back to you.