Warning, this guide may seem a little weird or crazy at first, but I have spent a very long time perfecting this build and it works in solo queue as well as premades, for the most part.
This build may vary depending on the skill of, and the amount of stun/stealth champions that are in play.
A side note, Master Yi benefits greatly from laning with Soraka or Taric, since I do not buy potions.
Starting out you are gonna want to buy Boots of Speed and put your point into Alpha Strike. Now go either top or bottom, whatever you feel is right. I usually go top but that's just me. You can go and scout the bushes to see if anyone is hiding in them ready to attempt a gank for first blood. You should be ready for this while scouting through the first bush and have Exhaust ready just in case. Better to waste it before any real battles happen then die. When the minions start to fight each other just keep killing them, trying to last hit as much as possible. Just keep Alpha Striking so that you will harass the enemy champions, but do not get too greedy! Always be in the start game mindset, Yi is a good end game champion, but early game he is very squishy. If the enemy pushes too far and you and your lanemate can take him out, by all means do it. Hit them with Exhaust and by now you should have atleast 1 point in Wuju Style, so active it and go to town. Remember that Alpha Strike is very good at hitting them without actually targeting them. So if they are getting too close to the tower, then target one of the minions that is or will be far enough away from the tower by the time you come out of Alpha Strike.
Make sure you get atleast 2 points in Meditate, it may seem like a waste especially if you have a healer like Soraka in your lane, but it's a life saver in the instances where their heal is on cooldown, or they aren't close enough to heal you in time.
By level 4 you should have enough for Berserker's Greaves, you can change these out for Mercury's Treads if you are facing a full team of stun's and slows. But Cleanse should be able to keep you alive long enough to massacre their team. So buy your level 2 boots and head back to your lane. Keep pushing the minions away, trying to get as many last hits as you can. Make sure not to over extend yourself, and always keep an eye on the mini-map and the chat, as people really like to gank Yi early, because of his glass cannon status.
When you get enough money go get your Emblem of Valor. Now you can take more damage from minions and not have to worry so much about being harassed. You can also jungle a bit when the enemy minions are pushed back to their tower. Don't be afraid to waste your Highlander at any point, it's really good at blowing through waves of minions, the added attack speed combined with your life steal is a pretty good healer, and it's cooldown isn't too terribly long. By level 12 you should be able to solo the Dragon very easily, so do so as often as possible, it's really good exp and gold, and you don't want the enemy champions to get any advantage at all.
At this point in the game you are still relatively squishy, so don't start anything you can't finish. Don't instigate anything more than a 1v1 and use the bushes to your advantage as much as possible. Don't think that just because you are behind a tower that you are safe, champions like Poppy and other tanks can charge through the towers hits and finish you off.
Remember if at any point you are taking continous damage from say Ignite or one of Teemo's mushrooms and you are a safe distance away from the enemy, use your meditate. That ability is Master Yi's most over looked ability bar none.
When you get your Phantom Dancer's you are beggining to become a force to be reckoned with. You can dish out fair amounts of damage but you can't take as much as you would like to, yet. You should be at around level 12-14 when you get your Phantom Dancer's, and you should be Jungling and killing your minion waves. Just remember that you aren't all powerful, so stick close to your team. The enemy is going to look for any opportunity possible to take you down a notch.
While building your Warmog's Armour try to buy the Giant's Belt first. The added health will help your suvivablity more then the health regeneration would. When ever I have enough money to finish off Warmog's it seems to be in the middle of a team push, one way or the other you need Warmog's to start getting the stacks ready. Don't be afraid of porting home and leaving your team 1 down as long as you tell them what you are doing. Most of the time they will understand and hold off till you get it. Now since you have Warmog's you are going to want to start getting those stacks as fast as possible. You should run between lanes after every wave till you get full stacks on your Warmog's. But keep a close eye and ear on the mini-map because there are alot of team fights going on at this point in the game.
This is when Highlander becomes your most deadly asset. You will be 1-2 shotting most minions and a maximum of 10 hits to kill the weaker champions. You should try to get the Golem Buff as much as possible. It may sound odd but you are going to burn through alot of mana and your mana is key to demolishing the enemy team. The beautiful part about Highlander is that every time you get a kill while it is activated all of your cooldowns will be reset, and for every assist your cooldowns will reset the equivalent of half. Meaning if you get 2 assists your cooldowns will fully reset! So if you activate Highlander focus on the weakest or closest to death champions first, you don't need to kill them because even if you get the assists it will fully cooldown. When in team battles your Highlander/Wuju Style super combo will clean house.
This point in the game is when god mode gets turned on, you will be dealing insane amounts of damage, while being able to tank insane amounts of their's. Remember level 5 Meditate gives you armour and magic resistance, and if the gap between you is that far apart you will be able to turn on Meditate and just sit there tanking their hits while the rest of your team does some of the work, and if you have the Golem buff it doesn't hurt to use it to max out your health.
When you have enough buy Youmuu's Ghostblade, it's active ability lets you gain movementspeed and attack speed for 4 seconds, adding another 8 seconds to it if you're attacking someone. It's esentially and extra Highlander just because. This point in the game it should be near completion. You should be in their base, or at least at their inner towers. If they have tanks with alot of armour, buy Last Whisper, if not buy Frozen Mallet. Last Whisper to give you that added attack speed, and of course to penetrate their armour. And Frozen Mallet because if you have your Highlander/Wuju Style combo going, they are slowed permenatly.
The game shouldn't last much longer than this but if it does, coordinate a Baron run for that extra ompff to finish them off.
And if it's really a run away game you can make my shiggles end game build. It will cost about 12k gold and you will lose all of your extra health but it's awesome and you will have 100% crit rate. You sell everything but 1 of your Phantom Dancer's and Youmuu's Ghostblade, then buy 1 Boots of Mobility and 3 more Phantom Dancer's. If you activate Highlander and Youmuu's at the same time while being out of battle for 5 seconds, you will be moving incredibly fast. If you do this on Twisted Treeline with Ghost and the Wraith's speed buff, you should have about 997 mobility. I haven't pulled this off in game but if you do I salute you.
Anyways that's my Master Yi guide, this build has been faithfull to me so I hope that it's faithfull to you aswell.