Master Yi Build
Not Updated For Current Season
The Black Cleaver - If you are facing realy tough tankers or heavy armored teams, this will rip them apart.
Guardian Angel - Imho the best pick for ranked games as last (6th) item.
In VERY VERY late game you can swap boots for:
Banshee's Veil - For heavy caster teams.
Last Whisper - Item for lategame armor penetration for ppl that face heavy tanky teams. Get this only if you already got Infinity Edge.
Force of Nature - for Heavy AoE teams (Fiddlesticks + Karthus combos for example).