Hello!!! I present you my guide for AP Master Yi!!! First of all I have to say sorry about my english but I m pretty sure you will understnd me!

Well for summoner spells i would choose Flash and Ignite... Flash allows you to teleport out of the battle after you have Meditated while Ignite ensures kills that you cannot get cause you are ap yi. I wouldn't really recommend other spells as they are the best!!!

When you are at level 1 you should farm and harass your opponents with Alpha Strike. If you get any damage while in levels 2-5 just meditate in the brush for a while ;)

Did you get your ulti??? You are ready to dominate them!!! Just finish your already low-life opponent with ulti,q and ignite and then finish the other as your Alpha Strike and ulti have been up because of your ulti "passive"

Later on, in teamifights do your alpha strike and then meditate until its up again. Your team will pick some kills and you as well.

Pros

Very Good harassing
Easy Multi-Kills
Can survive non-targeted ultis(for example Requiem) with alpha strike or meditate

Cons

Easy target for KnockBacks/Ups,taunts,silences, fears while in meditate
Needs experienced summoner to play