First off this is my first Build so fell free to leave comments. This is what i've worked up after looking over this build and that build trying them out and a good amount of play time. I've used this build in ranked matches but Yi doesn't break enough to the table to play all the time ranked. This build is meant to start out laned with someone who can solo. You have that small chance of quick First blood but if not you work on last hitting to about level 4-5 where I start jungle/ganking.

Pros
Massive ad dps
Good for killing towers

Cons
Squishy(till farmed or till BloodThrister

The runes I get are for straight damage. Yellow can be replaced with Armor or Dodge runes and works fairly good also.

Masteries are again for damage + in Def for a little surviblity but also makes it so you can run faster when dodging leading to more killing or faster running away.

I start out with vampiric scepter for my base lifesteal and so no gold is wasted it goes into Bloodthrister later on. I build Madreds for the anti tank + attack speed. If you arn't against a very tanky team you might want to go with wriggles for the free ward. From there i get Infinity's edge. Here you can go Bloodthrister first but Infinity's edge will pay for its self faster, and as long as your not getting focused you start to shine doing tons of damage in little time. After Bloodthrister and Infinity's edge are done I use Black cleaver for added armor pen, attack speed, and damage.

I get exhaust and flash both for chasing and for running away. these to along with your ult let you be able to get in and out when you want. Ghost and cleanse are also viable replacements for ether/or.

Once I get around level 4-5 I have enough for razor's to make jungle much easier. I start out with red buff then wraiths port back get a hp pot. Then I go get blue using hp pot if needed and then go on to gank(more often then not lane top and gank bot to start)

The only thing I see Yi bringing to the table in ranked games is his ability to carry against non CC heavy teams. That along with being able to kill towers quick alone, but in higher elo there is more map awareness and less chances of that happening. There is also always eating up noobs =)

So all in all this is how I play Yi. He is a very fun to own with(Love hearing Penta kill!). His ult makes it so aslong as you have health and mana your still chopping away at them even after first one is busted. When being chased if you can split of so only a squishy is chasing you is the best. turning around waiting in a bush just to destroy them before they know what happen. Feel Free to leave me comments on what you think and how you did if you tried my build. Enjoy