Hi, this is my first guide, so feel free to comment and rate. I will be happy to hear all of constructive criticism.
Master Yi is the fastest champion and IMO best to build a combination of attack speed and critrate and critdamage. Our goal is possibility to take out almost any enemy in few seconds, and be able to chase almost anyone.

Pros:

• Extremely fast - surprise your enemies with jumping between lanes and chasing them like a mad man!
• Cooldown reset with ultimate skill - if you save your mana you can take out enemy and then run with no fears of being slowed (God bless this amazing ultimate!).
• Passive skill can give you in late game almost 1k damage in less then a second.
• Wuju Style adds you a free damage, and after cooldown reset you have +105 attack damage for few seconds. It's even more than Bloodthirster with max stacks.

Cons

• Very squishy.
• Easy to take out with CC.
• Not very useful in big team fights.
• Annoying mana lack.
• Needs to feel the right moment to get in and out team fights.

Flash for easy getting away when ganked. Also good for getting away from when chased - just flash through wall.
Exhaust for chasing enemy when we trigger on ulti to fast, or in early game to get some easy kills. Can be used like a defensive to reduce damage you take by reducing the targets attack damage by 70% (don't use it against casters, it won't have any sence).
You can consider taking Ignite instead of one my those above, but in late game it does kinda small amount of damage.
IMO my combination is the best.

Kinda classic. I won't explain it with beautiful words and crazy amount of text. Just as it is...
Marks for armor penetration = more true damage - we are building a AS/CRIT champion.
Seals for mana regen = get rid off annoying mana lack.
Glyphs for magic resistance = for not getting nuked.
Quints for additional HP = for being less squishy.

Our base is critical hit rate. We are aiming for 85%.
What's more: our attack speed will rise above 2,000 without using the Ultimate.
We have to chase our enemies too. So movement speed is kinda useful too.
To reach this three thing we have to buy double Phantom Dancer, and Berserker Greaves.
OK, but what with attack damage? Infinity Edge, Wuju Style and double Bloodthirster will cover it.
Bloodthirster also gives us amazing life steal %. Combine it with our attack speed and damage. We will be able to kill Baron Nasher alone. :D
You can consider buying a Frozen Mallet instead of one Phantom Dancer or Bloodthirster if you don't want to be to low on HP. The slow doesn't matter. We will overrun EVERYONE with double Phantom :D.

Our primary skill is Wuju Style. We need every additional point of AD. The trick is to trigger it on in good moment.
Also very important is Yis ulti and Alpha Strike.
What's important. We don't use Alpha Strike as a way to do some bad things to enemies. It's our way to get closer to enemy.
Skill called "Meditate" with my build is useless. The 50% of life steal from double Bloodthirster makes us almost immortal.

For me Master is something like assassin and pusher. You can't jump in the middle of big team fight, because you will die in less then a second. Your goal is to sneak from behind, kill casters and runners.
The next way to play is pushing the towers. But for this you need to know where your enemies are. You don't won't to be ganked, don't you?
Example: enemy team is busy destroying your turret on bottom line? Ask team to defend this turret. Meanwhile you can go somewhere else and destroy a turret. Even without minions. Trigger on ultimate, and Wuju Style and be happy. :D Then go to kill blue golem, to reduce cooldowns and be even more happy.
As i said your Ultimate skill, Highlander, gives you a chance to reset all of your cooldowns. Is the Wuju Style skill description we can read: "(...) this removes passive bonus until the skill is ready again". So when we trigger on our ulti and Wuju Style, then kill someone the cooldowns will drop to 0, so for just a few seconds you will gain both - passive and active bonus attack damage from Wuju Style. For this short amount of time your damage is even higher!
Oh, almost forgot. Don't spam with Alpha Strike to avoid loosing all of your mana.

So... To sum up. You are level 18. Got all of your build items, all stacks etc...
Attack damage - 390+35/70/105 (passive/active/active+passive) with Wuju Style.
Attack speed - something about 2,220, without using ultimate.
Critical hit rate - 85%
Movement speed - something about 490, without using ultimate.

Have fun! Rate and comment. Feel free to criticize.