This is my first build, so please be gentle and excuse my English. ;)

I decided to make this guide because there is a lack of jungle guides for Master Yi and I want to explain you my way of playing Master Yi.

Why Jungle Yi you may ask?
Yi is okay in lane, he can harrass a bit, can make a bit dmg, but in the jungle you can find real domination. After getting red, you have nice CC for getting first blood, and also without red you can force the enemy to waste their flashes ( Alpha Strike) or easily kill them with Exhaust. A gank with Alpha Strike, Wuju Style and red nearly always results in a kill for you, if the enemy doesnt use flash. The surprise is a big advantage for Master Yi.
And after getting a few kills in Early game you DOMINATE in Mid and Late game.

Pros

-Strong in Early and Late game (Mid game CAN be a problem)
-Really nice dmg output
-Snowballing like hell (But no need to)
-Kill ..... Doublekill .... Triplekill ... Quadrakill .. PENTAKILL!!! (with Highlander no problem)
- Meditate ?!

Cons

-Squishy like hell (You live from your livesteal)
-Will be focused if the enemy is smart
- Thornmail is a real problem
-Mana problems

Runes

For my runepage I choose 9x Greater Mark of Desolation (Armor pen is always nice), 9x Greater Seal of Attack Speed, 3x Greater Glyph of Cooldown Reduction (for some CDR in early game) and 6x Greater Glyph of Scaling Cooldown Reduction. Of course armor pen Quints Greater Quintessence of Desolation.

Its your decision of you wanna make it the same way, or if you wanna choose different runes. Normal jungle runes are nice too, but I prefer this compilation.

Summoner Spells

My Summoner Spells are always Smite (you need it in jungle, Yi isnt strong enough to manage jungle without that) and Exhaust because Master Yi lacks CC if you dont have red buff.

If you dont wanna use Exhaust I got some alternatives for you:
Flash
This Summoner is always nice. You can use it offensive and defensive. A good decision.
Ignite
Its okay, but you can use this only offensive.

Summoners which you shouldnt use:
Ghost
Master Yi has a movement speed of 450 with Berserker's Greaves and Phantom Dancer (And with Highlander you have 550). Riots Softcap on Movementspeed will make Ghost nearly useless, believe me.
Clarity
Sure, you got some mana issues but... no... not really?
Teleport
Are you really sure about that? There are no real cons against that. But you can choose better ones.

Under construction, guys. Wanna add some situational items.

First skill Alpha Strike and buy a Cloth Armor and 5x Health Potion.

1. You will start at the little Golems. Use Alpha Strike. Smite the one you are fighting and kill the other after that. Use a Health Potion here.
Skill Wuju Style.

2. Wraiths. Alpha Strike them, activate Wuju Style and focus the big Wraith. Use a Health Potion here.
Skill Meditate and use it (if necessary).

3. Wolves. Alpha Strike them and focus the big Wolf. If you want you can use a Health Potion here (you have to if Alpha Strike didnt proc the hole jungle).
Use Meditate (if necessary) and go on to blue.

For blue you need 3/4 of your life or you will die. If you dont have enough life you can kill the two little minions, go back and kill blue after that. Its no shame.
Otherwise:
4. If Alpha Strike procced a few times you should have 120 Mana, if not you should wait till you get 80 Mana and use Alpha Strike (if you have enough Mana use now Wuju Style). Use a Health Potion. Just focus the Golem and use Smite if he is low enough to ensure that you get the buff. Then kill the two little minions and go back.

Buy a Long Sword and one Health Potion (perhaps you will have to wait a few seconds for some gold) and then start the route again (Dont use Smite for the golems!). You should have 2 Health Potion.
Use your spells! You got blue! And always use Meditate to save one Health Potion for red. You will need it.
If you cleared the jungle again go to red. You should have again 3/4 of your life, or you made something wrong. Use Alpha Strike and the Health Potion then focus the Lizard. Smite him when he is low enough and kill the two other minions.

If you see a really good chance for a gank now: DO IT! But you should be careful, you are low now. Better you go back and gank after that. You can also gank a lane where the enemys have full HP. Your dmg is really nice with activated Wuju Style. But DONT towerdive, you will die.

Alpha Strike:
This spell is really nice for jungling. If you are lucky you can clear the jungle incredibly fast. If it doesnt proc... Dont care about it. Its usefull but not necessary.
In fights you can use this spell for chasing people and to start a gank. Remember that you will land at the target you choose. This can be really awefull if your enemy runs into his team when you use this spell. Be careful with Alpha Strike.
NOTICE!!! After an Alpha Strike Yi will focus his previous target. In the WORSTCASE this means that Yi will run back to the minion (or whatever) he attacked before. So dont forget to make a right click on your new target!

Meditate:
This skill is sooooo awesome! On lvl one you get 100 armor and magicresistance and on lvl 5 300 (!!!). Can you imagine how much that is? (With 300 extra armor and magicres you just get a 1/4 of the dmg).
Some examples for using that spell:
1. You are low and running away. Caitlyn uses her ulti ( Ace in the Hole) on you and you know you will die. Just press W and pray, if you are lucky the extra armor and magicres will save your ***. Same with Karthus ulti ( Requiem).
2. You are fighting against a Fiddlesticks. When he starts Bountiful Harvest without fearing you, you can easily use Meditate and laugh at him as you heal yourself while he gets a **** out of that. When Drain is over you can go on attacking him.
3. You were ganked in the jungle and your teammates are on the way, but you know you wont survive long enough? Press W and hope you will survive. It can save your ***!
(And that are just a few examples)

Wuju Style:
This skill is also really nice. It gives you 35 extra dmg at Lvl 5 which doubles if you activate it. Thats a lot. But notice that you get a **** when Wuju Style is on CD. The extra dmg is gone for that time (as well as the passive). Activate it and pwn your enemy.

Highlander:
This skill is awesome for chasing and getting some double kills or more because ALL COOLDOWNS are refreshed when you get a kill while Highlander is active.
When you use it, you get extra movement speed and attack speed while you cant be slowed. The enemies use Exhaust? Pfff! Doesnt matter! We got Highlander! Also nice for escaping.

And Master Yi lived happily ever after...

Thank you for reading my guide and please give me some feedback. Constructive criticism is welcome! (Especially for my English :P)

Have fun while trying this build. ;)

With kind regards
Zeeker