Hey, this is my first build. I write this build for one of my favorite champions, Master Yi.

Since I mostly play 3v3 I will focus the this build mostly on 3v3 games. Remember, this does not mean that the build would not be effective in 5v5.

In my opinion Master Yi is one of the best 3v3 carries currently available in the League of Legends. So read on...

Pros
As fast as a racecar ---Zzzzuuuuu
Crazy damage on most champions
Great jungler
Awesome farmer (Alpha Strike)

Cons
Squishy
Disables, Very vulnerable to stuns/fears/etc...
Good use of Thornmail counters him well

Master Yi is a great 3v3 jungler, and a great jungler overall.

Early game jungling
The second you buy yourCloth Armor and twoHealth Potions head down to one of the jungle creep spawns near the middle of the map.Smite the Blue Wraith or the Golem depending on what creeps type of creeps spawned, then use yourAlpha Strike and finish all of the creeps off. Use oneHealth Potion here if needed. Now go bot and help your partner lane until yourSmite has cooled down. Once it has, go back and kill the second pair of creeps. Repeat this until you have enough forWriggle's Lantern.

Mid game jungling
Here's where the fun comes. With your lantern you will be able to kill all of the jungle creep easily due to your lifesteal and damage chance. You can solo dragon at about lvl 8. If you are fighting it and are having trouble, you can just use your ultimate and its yours. Try to get the dragon for your team as much as you can, and use your lantern to place wards in important places such as red buff or dragon so that you can predict an incoming gank or make your own. Always remember to pop-out of the jungle to help your team get kills. Your ultimate is great for chasing down enemies.

Late game jungling
During the late game you could critical 900 on monsters due to your lantern and critical chance. You will EAT all of the creeps. Literally. By now jungling would be pretty much useless to you and you should do it only if you need the buffs or a little big of cash.

There is a number of items can can help you defeat your opponents. Consider substituting them for the lantern if you are losing against the enemy team.

Against Attack Speed/Attack Damage > Frozen Mallet - This will greatly slow the enemies Attack Speed and will give you an advantage when they are running away or are fighting you.

Against Armor/Thornmail/Tanks > Last Whisper/The Black Cleaver - This will HOPEFULLY allow you to penetrate through most of the enemies' armor, enough to let you deal some serious damage.

Against Master Yi > Thornmail - This will give you great advantage if you are facing another Master Yi

Champions like Rammus or Fiddlesticks with disables like taunt and fear will let Master Yi dominate the enemy team as they will not be able to focus him. Try to work with your team and attack the enemy while they are disabled.

Popping out of the jungle every now and then to gank an enemy is a great way to give your team an advantage in kills. At level 6 you should have your ultimate. Use it to target and kill squishies in early game.