Master Yi is a champion of many possibilities. He can be played either AD or AP. When played AD, he can be glass canon, tanky damage dealer or offtank. I think its best to build him as tanky damage dealer. You still have absolutely amazing damage, while having decent health with good MR and Armor.

Keeper of the ancient art of Wuju,Master Yi is a mystical warrior from the isle of Ionia. He descended from one of the few tribes dedicated to the preservation of Wuju, a martial art founded with the principles of absolute spiritual awareness of one's self and one's enemy. When the armies of Noxus invaded Ionia, Master Yi joined in the Ionian defense to fight the craven enemy, bringing his village honor through his unparalleled mastery of the blade. The ensuing battles ravaged the land, but no conflict inflicted as much horror as the day the armies of Noxus closed in on Yi's village. Left undefended, the village became the unfortunate test subject of the latest invention by an up-and-coming chemist, now known as Singed. The remains of the village that Master Yi returned to were so horrific that it remains a festering scar on Ionian history. To this day, no Ionian will ever publicly speak of what occurred.

After the Noxian invasion was contained, Master Yi fell into a deep isolation. For years, he trained morning to night, speaking to no one and refusing offers of consolation by fellow Ionians. The only thing stopping him from madly charging into Noxus battle lines headfirst was his pledge to keep the Wuju style alive. Even though he seethed with impatience, his rage became a tool for sharpening his practice of Wuju, developing stronger and deadlier skills for his eventual vengeance. The only thing that roused him was news of the League's formation, and Noxus's subsequent enrollment in the League. Master Yi now brings his mastery of the blade to the League of Legends with unflinching purpose: to avenge his kinfolk and end the predations of the Noxus once and for all.

"The art of Wuju lives on in Master Yi, and is plunged through the hearts of his foes."

Pros
Great pusher/tower/farmer destroyer
Pretty easy to learn overall
Great escape/chase mechanism
CD resets/halves when you get a kill/assist(if Highlander active at that moment)

Cons
Vulnerable to disables like blind, stun,suppress...
Low HP poll until you get Frozen Mallet or other HP item)
Not so great in team fights

I want to express my gratitude to everyone that reviewed my guide and gave constructive feedback.Also in conclusion I hope this build helped you on your path of becoming a good Master Yi player.