Ok ,as the title says so this is a build for beginners with master yi.
he is 1 of the strongest and best champions and he is cheap only 450 ip and he is a champ that is pretty easy to play. so thats why i made a build about him. Here We Go

As i say this is just a beginner build so u should not buy any runes until you lvl 20 and can buy Tier 3 runes because Tier 1 and Tier 2 is useless.

I choosed heal and ghost because yi is pretty fast with ghost and you should play very cowardly
and dont let them get you thats why i get heal.

First of all u need abit damage so buy 1 Long Sword. When u have enought money to buy 1 more then buy 1 more and when you have cash for brutalizer then buy it. now u need to help your self survive so u buy berserker greaves they are god when ur farming and running. after berserker you farm and get around 1200 gold and get Zeal soon you farm gold till you can get the whole phantom dancer. now u are strong enought too beat em up but u have to get much stronger to beat em more easy so u get a blood thirster because you need more damage and lifesteal so first u get B.F Sword and after that vampire scepter soon you get ur whole blood thirster.
Now u need some crit and more damage so first u get 1 more B.F Sword after that Pickaxe and cloak of agility and u have ur INFINITYS EDGE!!!! now ur unbelieveable but they can easily kill you if they gank so get something Tanky, and the best 1 is sunfire cape it make so you have more hp and armor.

because meditate is useless and alpha strike can get you really much money when ur farming so its really good and wuju style gives u really much damage so you should put it on when you are hunting champions or turrets and highlander is good to survive and help ur mates to survive so you can run there fast.

as i said on the introduction u should play very cowardly.

ya play very cowardly and dont dive turrets and play safe if you are fighting ranged champions and u should never go mid at 5v5. and a good tips is to check the tips on ur char.and a good thing is to jungle when u have blood thirster because u can get all the jungle monsters easily except Baron.