this is my first build so please be kind, this is a build of how I play him so if you judge by how you "want" to play him then navigate away from this build and do not vote with that said let's move on

Greater Marks of Desolation - your yi you need armor pen nuff said
Greater Seals of Replishment - early game yi is VERY mana hungry so with that said the mana regain is rather nice
Greater Glyphs of Celerity - everybody likes CD reduction right? and with that nifty self-heal it bodes well for your laning phase
Greater Quintessence - again more armor pen? yes MORE ARMOR PEN you need it you right click to win!

ALTERNITIVES
The marks i wouldn't trade out for anything except Greater Marks of Alicrity
again the seals in my opinion are not replaceable but Greater Seals of Alacrity work nice too
also the glyphs the only replacement for these IMHO would by Greater Glyphs of Alacrity
finally, the Quintessences are not replacable except by Greater Quintessences of Alacrity

Ghost - combined with your ultimate you can catch up to about anyone except maybe rammus
Exhaust - your a DPS/AD put this on one of their squishys and just right click to win

Possible Alternitives

Teleport - it's nice to have map dominince so yea this could work
Ignite - to finish off those runners and get some extra kills
Heal - for a nice FB for the extra gold and to bait in enemies who believe that they can turret dive
Cleanse - to get out of those sticky situations
Flash - a nice alternitive to either get out of a gank or to catch someone

What not to get

Rally - let the supports get this you need your slot for more important spells
Revive - you shouldn't be dieing that much so what's the use?
Fortify - let your tanks get this you don't really need it
Smite - unless your jungling you don't need it
Clarity - unless your spamming your abilities (which you shouldn't be doing) you don't need this

Pros:
Deals out great damage
Can self heal
combined with life steal is almost un-killable
Can lane with long periods of time
With your ultimate can catch just about anyone
Your ultimate lets you able to not be disabled
Cons:
Focused down quickly
Blinds are your downfall
before level 6 you are very supceptable to ganks
Is very item dependent

Berserker's Greaves - gives you movement speed and attack speed
Phantom Dancer - more movement speed and attack speed
Infinity Edge - Attack Damage, and Crit chance? nice plus 50% more crit damage
Hextech Gunblade - gives you a nice bit of ability power for your meditate, also you get lifesteal YAY
Madred's Bloodrazer - ok more attack speed and attack damage which is nice but what makes this item nice is the passive that does 7% (i might be wrong but it does somewhere around there)
Frozen Mallet - attack damage plus hp and a nice little slow so they can't run anymore :)

Alternitives

Banshee's Veil - HP, mana, and magic resist? yea ok that's rather nice but what this item is here for is it's passive which is to block 1 spell which could be a killer, like ashe's enchanted arrow or a blitzcrank grab
Black Cleaver - if your having trouble with tanks get this because it's passive shreds they're armmor
Wit's End - this item is for casters, it does magic damage to them and drains they're mana
Stark's Fervor - if you don't like the Gunblade this is a nice substitue and also if someone on your team doesn't already have one
Tiamat - gives you attack damage and it's passive is nice, it does splash damage to any surrounding enemies
Randuin's Omen - if your getting focused down ALOT then grab this
Guardian Angel - again if your getting focused too much then grab one of these
Sword of the Occult - if you feel your doing fairly well and can hold stacks up at atleast 15 then get this
Bloodthirster - if the gunblade doesn't suit and someone already has stark's then grab this for a nice percentage of lifesteal and damage

ok killing big minion rushes is one of the things yi is good at, thanks to your alpha strike at level 5 you have a certain percent chance of killing a minion instantly which is nice, next you can just right click to kill them all

if you want to jungle grab smite and exhaust, the jungle route i use is small golems -> wraiths -> wolves then rinse and repeat until about level 6 which is when you can get alittle gutsy and go into the enemy jungle

like i said before this is my first build so criticism is always nice (excuse my spelling mistakes) but yea this is the way i build yi i hope you like it, but i do not have any colorful pictures for you to look at i apologize for this