One of the best ap in league of legends.Like every other champion, there are a few ways you can build them, I personally like building my Kennen as AP. There are a few things that I do that i believe set me apart from a few other Kennens, and I like to think it's what puts me ahead of the other players.

What can I say, Magic Pen is Amazing for Kennen

The health per level will give you a-lot more benefit then straight health (past level 5) and Kennen needs all the survivability he can get

The ability power per level will also grant you a-lot more benefit then straight Ability Power (past level 5). Just helping him put out alot more damage, The only other blue rune i could see being decent is CDR, but it seems like a waste to me.

I've Tried Flat health, CDR, Magic Pen and Flat ability power Quints. I feel that 3 of these bad boys are AWESOME for early game, gives you that flat 15~AP that will help immensely for getting first blood. If you dont have the Flat Ability Power quints, your second best bet would be Magic Pen.

This items are most based on ability power witch is very important for this time of champion. Well.. first you need to start with dorans Shield after take the sorcere's boots to gain magic penetration, then u need to purchase the void stuff and will of the ancients to have spell vamp. After is important to buy rylai's Crystal Scepter to add some Hp then rabadon's deathcape to add some AP. At the ending look at your enemies and see what are they (ability power or attack damage). If they are ability power you will need to buy Abyssal scepter if he is attack damage you will nead Zhonya's Hourglass.