Ok this is my first build i made for this page I will try to explain best I can , hope you'll enjoy :). First build is abut being carry and getting kills like crazy and second one is when you are lacking a tank to help your fighter maintain fight.

So for rune i take flat armor and magic resist per level for easier jungle (also its preety when solo top) also armor pen. runes and flat dmg for ganks ... for masteries I go 21 in dmg and 9 in deff .. which i think is imortant is that you take improwed summoner spell for exhaust for easier ganks . For jungle i think best is exhaust ( which i think is one of the best spell for chaseing killing and running away) also is preety good for solo top , take smite ofc ( you will be able to do jungle without it but it is important for baron steals and such. When solo top take ignite instead of smite.

So in jungle its obvious to start of with Alpha strike because of its chance to do extra dmg to minions .. start on blue and right after you kill them take Meditate ... It should be easy for you to jungle from now on since you can heal with meditate whenever you like, later wriggle takes care of jungle for you... Solo top is prior. for ganks so ,try help him especially if he is alone vs 2 ( in rankeds it should be much of a problem because usually they got jungler too). Warn your fellow mates not to push much for easier ganks use your wriggle smart also you can buy more ward if you want to help team more

Start off with vampiric scepter (I think its always best to start with it on yi and similar champions) follow with boots of speed to speed up jungle and after wriggle it all goes really smooth.. 2x doran blades really give yi the ability to dominate in early game ( but try avoid risky fight untill lvl 6), after getting first phantom you should be able to kill most of the champions ( combined with ult and exhaust all are dead before they blink),Infinity is crucial when playing carry so get it right after 2nd phantom (if you ask me - speed+crit>dmg)by replaceing 1 doran blade.Replace other doran with Giant belt and complete it to Frozen mallet.. If the game really lasts long replace wriggle with Bloodthirster and boots with Guardian angel(because you dont need to run arround crazy like in early / mid game)

It is really important that you farm alot I know this is obvious but still some people don't care so much about farm but not only that you get money you leave your enemy behind with exp...

since this was my first build please pm me what you think i will make corrections also please someone send me how to put in links to items , runes and such because i am new here thx :)