This is where I will post changes to this build when new patches are released.

Q - Alpha Strike - Master Yi leaps across the battlefield striking up to 4 enemies, dealing 100 / 150 / 200 / 250 / 300 (+100% of ability power) magic damage to each enemy with a 20 / 30 / 40 / 50 / 60 % chance to deal 400 bonus magic damage to minions.

Great way to farm, harass, chase, get close up to the target for your hit with the lich bane bonus.

W - Meditate - Master Yi channels, restoring 28 / 56 / 84 / 112 / 140 (+80% of ability power) every second for 5 seconds healing a total of 140 / 280 / 420 / 560 / 700 (+400% of ability power) health. He gains 100 / 150 / 200 / 250 / 300 armor and magic resistance while channeling.

Great defensive and survivability skill. Allows you to lane for a really long time as well as giving you the sense that you have double the amount of HP that you really do.

E - Wuju Style - Passive: Increases physical damage by 15 / 20 / 25 / 30 / 35
Active: Master Yi can activate this ability to double its effect for 10 seconds, but this removes the passive bonus until Wuju Style becomes available again.

It's always nice to know that your attacks hurt.

R - Highlander - increases movement and attack speed, ignores all slows, upon killing an enemy champ you refresh all cooldowns, upon getting an assist, you reduce your cooldowns in half.

This lets you alpha strike after alpha strike if you're killing enemies with each.

Doran's ring is by far the best starting item if you are planning to play Master Yi as an AP caster. Around 5 minutes in, if you have been constantly harassing the enemy champion(s), you will find yourself constantly at 50 mana or so. I suggest getting another Doran's ring just to boost your hp, ap, and mana regen and the cost is extremely efficient. After your boots, you should be getting a Kage's Pick to later build into a Morello's. Rabadons Deathcap is the next item to build and should be easily gotten by the 20 minute mark. A Lich Bane combined with your gap closer will increase your burst damage by a huge lot. Afterwards, depending on the circumstances, you should aim to get a Zhonya's or Abyssal scepter. If the opposing team is composed of mainly Attack Damage I would suggest getting your Zhonya's first but if their Magic Damage output is what is hurting you, build an Abyssal Scepter. Your final item should depend on whether the other team is building tonnes of Magic Resistance or not. If they are I would suggest getting a Void Staff otherwise finish with the other one of the two items previously mentioned. (Abyssal Scepter or Zhonyas Hourglass)

Maxing Alpha Strike is obvious as it is your primary source of damage. Skilling your ultimate at its standard levels will boost its duration and then maxing meditate as it gives you insane Armor and Magic Resistance (300) by level 5. Meditate will also heal you up in as quick as 2 seconds when you have maxed your build as it heals you for the base amount + 4x Ability Power. When you are level 18, your physical damage will be outstanding for an AP caster.

Flash and ignite are what will get you kills and what will help you get away from being killed.

Ignite is your biggest nightmare as it will reduce the healing received from meditate by a significant amount.

Pros
- Good poke in lane
- Fast farmer
- Natural damage
- Built in Zonyas but not immune to stuns
- Can chase anyone
- Cannot be chased down
- Is still a decent right clicker late game with his Wuju style damage
- Can deal huge amounts of damage every 6 seconds to 4 champions

Cons
- Can get nuked down if the opposing team has several stuns
- Item dependant
- No slows or stuns
- Gets countered if the enemy build a lot of magic resistance.

When laning, make sure to alpha strike minions and hope that it hits the champion on the way back rather than diving at the champion. Try not to waste your meditate at an unnecessary time during a team fight as it can be a crucial lifesaver.

Generally you would want to be in the mid or top lane but it is not the end of the world if you end up in a duo lane.

Occassionally, get a elixer of brilliance for the CDR and extra AP.

Just because you used Alpha strike doesn't mean you can't do anything else. Yi has one of the best base damages in game, combined with his ult and wuju style, he can still pack a punch.

You want hard hitters, stunners and bursters to be on your team and should hope for no stuns on the other. While you meditate, if the enemy are mindless, they will try to kill you as you regenerate to full life. During those 5 seconds your team will easily tear them to shreds.

If you think your hp pool is too low, buy this. The slow could help as well.
If you're confident that you can continue to own, (that's if you are currently) this will give you a huge boost in ap.
More cd but I think blue buff, Morelos and your masteries will keep you at max cooldown reduction. So I would prefer 20 Magic Penetration over this.
If you don't think you have a large enough mana pool, you can get this.
More burst, meaning more ganks. But with the new patch, Kage's lucky pick can be built into a Morelos.