I admit that I was very lazy about the description... and I have added extra LS at the first, but as for the extra AS, how expensive it is, and CDR/dodge runes:

Extra AS: The boots are taken away at the end, because if the game lasts that long you will definitely have enough cash to sell them. So you only end up with 20% extra attack speed. The phantom dancers add a little extra AS, but it is way worth the critical + dodge chance + movement speed that PD's have.

Expensive: All builds should be expected to be expensive, because it is very rare that the game will last long enough for you to buy all the items and even if you do end up buying all the items then whats wrong with that?? If you have enough money then why not buy something with it? A cheap build isn't even an advantage.

CDR/Dodge runes: Critical damage is going to be extremely useful, especially at the end when you critical almost ever hit. Those runes add over 30% increased damage, and when you critical almost every hit then it is literally 30% increased damage! I was going to make the other runes add critical strike damage as well, but that is not what that particular rune specializes in, so I went with whatever was their strong point. Which was cool down reduction and dodge chance. Nimbleness definitely would be an advantage, but it was either nimbleness or awareness, and 5% extra exp would help keep you ahead of your enemies, so I considered it a better choice. Besides dodge chance is still very usefull even without it.

Why is it that almost everyone that build Yi, has to have the most expensive items?

This is by far one of the most costly builds. It comes out to 17,595 gold. I can spend 7k less and get the same, if not better results. And no boots... Thats the best part. There is nothing better for the other team than a Yi with no boots. You can Dodge all you like, but that dodge wont help with mage spells and AoE effects.

Too many things wrong with this build. -1

Yi caps AS at 110% from items.

With your items:
2xPD and Last Whisper you are getting 130% aaand another 25% from boots that is total 155% so makes it 45% over AS cap.

Totaly wasted money.

CDR runes? What for?
Dodge runes while you dont go for numb mastery?
Crit damage vs ArP Marks... well ArP is far more superior than crit damage.

As Tinaby said, getting lifesteal that late means you will be quite useless early/mid game. You will hit fast and crit, but you wont push or jungle that effectivly.

Your weak point is the description also, or i can call it no description at all.
It is nice you had a good score on lagged game but tbh you are the best person for lag games. While casters are punished by huge lags you will still hit hit hit... so tbh that was a handicap for your opponents not you.

Well, putting lifesteal in the main points while it goes only from bloodthirster you make at last is just a joke.

In most games you won't even get one if you're going for all those expensive items before.