First of all, i got to say, that there are alot of different builds for Master Yi.
But i picked this one because, its a good working build versus variable enemy Teams.

Im a german guy, so im sorry for my english ;-)

I like to have some suggestion about it, sure i will try, if someone will explain me why to change something.

Pros:
- Hard Carry
- Superb gank abiltiy
- Strong Tower killer
- Good damage in early game
- Hard to gank (with a slow)
- Fast famer/pusher

Cons:
- Very squishy
- No CC
- A bit luck based thru Alpha Strike

Jungle yi is a bit risky, because you dont know if u get the bonus Dmg from your Alpha Strike.

But if your on a Lane you can have enemys on it, which really kicks your *** from the lane.

Thats why i prefer save farm, and a really nice ganking ability.

Called Jungleing!

First of all say that your Team have to cover you at blue. this is very important!
if you get ganked you have to go back and its hard to get back in the game.

So if your not getting ganked this is the way to do it:

1.) Alpha Strike on the buff Golem and after first damage, immediatly put your potion on.
When you getting the Bonus dmg you have no problem with the buff Golem.
If not its getting close. Your Alpha Strike should be up when you are around 250 HP.
Use it and smite the golem. Then it should be done. Kill the smaller creeps with auto attacks.

When your potion is out always activated your next one.
Go to the wolf camp alpha them and take them out without your "E" skill.

When you get to the Ghost camp you alpha again and activate your "E" skill.
Then recover a bit Health before getting the red buff. Wait till you have around 450 hp.
Alpha him again and when hes nearly around 2/3 Hp activate "E" again (other way a bit dmg is gone). Depending on how often you get crits or alpha bonus dmg you are able to kill the Golem camp too.

Now its time to shop.

Get the boots, 2 health pots and a ward. Then its ganking time. If you wasn`t able to kill Golem camp do it before.

Then look if your able to gank bot or mid, if not farm more.

How to gank:
Look which summoner skills they have. It would be useless to attack someone with Flash. Wait till they pushed the lane a bit and then engage with activated Ghost and Alpha Strike on your target. After landing beside the enemy get your "E" skill on, to do the maximum dps. With the red buff and Ghost its nearly impossible to get away!

After it get your Ward up at the Dragon.

Then go on jungle farming. When you finished madreds razor its quite easy.

Always try to gank or hold lanes if possible.

The hardest part while playing Yi is the team fight.

When you dominated early game, go and fight, but just wait till most of cc is out.

Your team will hate you maybe for waiting, but you have to play save, because you are squishy as hell. Always try to kill someone, even if it is a Killsteal. You need it to have your Ulti up again.

How to go in:
Always try to get to their squishy champs. Running in with ghost and your ulti combined with Alpha Strike allows that easily. Best thing is when you dont need to Alpha.
When you attack, activate "E" and activate your Sword of devine and see how fast people can die.
While fighting Alpha Strike as often as you can.
They will losing their focus on you for a moment. This allows you to be longer in the fight.

The best thing you can do for your team is often not to fight in clashes (except late game):

KILL TOWERS

One Tower kill worth 150 Gold for everyone in your Team. Thats 750 Gold. Even if you would be able to kill alot in fights, its still better to have your Teammates get fed too.

How to kill towers:

Wait till your team is gathered and almost all enemys too.
Then went immediatly to the farest pushing lane.
With your Alpha Strike you can push faster and you have just a nice Damage bonus thru "E".
Activate your "R" and "E" and get the tower down.
Always have map awareness for incoming enemys. If they come, you have Ghost to get away.

With a bit of Luck you are able to kill some low Hp Heroes on your way back to your team.

I started different builds and this one works best for ME.

You could change Sword of Devine for Youmu`s, but i prefer the bonus damage thru sword of devine.
I dont think the movementspeed is important and the only thing that u rly could need is the attackspeed buff and cdr.
Because this built doesnt relay on pure dmg or even a cdr is needed. Just the pure attackspeed is what u going for. That maxed out by sword of Devine, you always have improved your attackspeed and get the 100 bonus dmg.

You could play Yi on Crit but engaging tanks is hard with it (and u need much more Gold).