This is good throughout the game and it is difficult to protect screens, because this is both (ap and ad).
when you are get to sorcerers shoes, sell sheenand buy rabadons deathcap(+155 Ability Power UNIQUE Passive: Increases Ability Power by 30%)
if you take this build you need to be 1v2 if you can not last hit

This build is not ready!!!

Master Yi is the end game champion, so do not take unnecessary deaths in the first game, and try to gain as much as possible of the last hits to get the best possible items at the outset, because the build in surviving yi is pretty useless to the team.
with yi is good to be stunned, because when yi Get he passive (a double blow every seventh hit), what make wery much damage to enemy player(1 lvl yi do 2 x 84 damage = 168 damage + alpha strike= about 250 damage)
Yi Master Cleanse is good to have, because yi is a small hp dps Champion (Cleanse may immediately remove all of the stunning, Taunt, etc.)
the final game of yi is just a crazy end-game, but you should not still go solo if you do not want to die.
Ps do not go into battle first, but stay behind and wait for the other champions sustainable income.

If your opponent has at bad tanks(rammus, malphite)buylast whisper(+40 attack damage, and +40% armor peneration), if your opponent has at large hp champion (fladimir, singed, ghogath)buyblood razor(having a certain percentage of HP from the hit), and if your opponent has at lots of stunts and taunts buy mercurys tears(reduce stuns and taunts)[/b].
If you goes bad, buy banshees veil(+375 Health +375 Mana +50 Magic Resist UNIQUE Passive: Blocks one negative spell every 30 seconds)(Note. Buy this items after your phantom dancer, because if you buy this items in early game, you don´t do so much, your attak speed and crit. chance is wery low

Build 1
this is really good build for the middle and the end game build, which can quickly togetherand it is easy to play.
Build 2
this is harder to play build, who is also more difficult to assemble
Ap build
this is really good at the beginning, and this can be used 1 v 2 and the middle (yi doing a lot of damageto alpha strikeand get back to meditateon the lost hp)
Hybrid buildThis is good throughout the game and it is difficult to protect screens, because this is both (ap and ad).
if you take this build you need to get last hits

Here is the various summoners spells the pros and cons

in my opinion the best Summoners spells are:

Pros:
ExhaustDescription: (Reduces a targets Attack Damage by 70%, Ability/Item damage by 35% and slows its Movement Speed by 40% for 3 secondsand cooldown is 210sec.)This Summoner is my opponion the best summoner to Yi because you can survive to wery easily if someone Hard Dps attak to you(e.g. Tryndamere.
Cleanse...........

Dps master yi

Marksand QuintessenceArmor Peneration Runes:Armor Pen. Runes are good for yi because yi do 31-more damage to the enemy champion and its lot early game (Caitlyn has early game only 17 armor so its lot)
SealORGlyph+0.1 mana regen / 5 sec. per level (+1.8 at champion level 18) or +0.08 mana regen / 5 sec. per level (+1.44 at champion level 18) :Mana reg. runes are good for yi Mana problems always in the central game so its perfect to yi because yi skills take lots of mana.
Glyph-0.65% cooldowns:Cooldowns Runes are good for yi because yi wuju style ([Passive]: Increases physical damage.
[Active]: Master Yi can activate this ability to double its effectiveness for 10 seconds, but this removes the passive bonus until Wuju Style becomes available) so you get wuju stylepassive get faster and you can spam alpha strike skill.
Sealdodge:dodge Runes are great for yi because you dont get someone physical attacks,BUT if you use to dodge rune you would be better to buy to Ninja Tabi(+25 Armor +12% Dodge Chance) and introduce to evansion(Increases dodge chance 2% by 3/3)and Nimbleness(On dodge, increases your movement speed by 10% for 5 seconds)

Taric has very good heal for you and he has good stun(taric is best laning partner to yi in my opinion).sion has good stun