After all those changes in season 3, master yi was greatly affected, and the old and even new build i tried were not that good so i tried to make a new one and it worked very good so sharing it will not be a bad idea.

although i do not care about this cause I'm lvl 22 (don't judge me i have school so i cant play that much) i put what i think will be good with the build.

you don't have to choose between ap and ad, build your own don't depend on others just get ideas.
for active items:
1.wriggle's lantern: the place you put these wards totally depends on the game, try places where you think they will gank you, or near baron at he right time, every where most necessary.
2:hextech gunblade: directly after alpha strike, or in 1 vs 1 fights.
u should know this is for noobs.
edit: at end game you can sell wriggle's lantern and buy another strong item against different enemies.

i did this because nobody use master yi these days, he is the strongest champion if you know how to play.
and please if you have something just say it in a way that helps, don't start commenting ****.