This is my first build... any advice for how it could be easier to read would be nice. Kennen is easily my favorite champion, i played him when he was free and bought him as soon as i could afterwards. kennen is the most balanced champ iv ever played. what i mean by this is that if your team sucks, you can still do well. once you get good with kennen, you can and will turn team fights. you can stun their entire team when you ult, and then from there choose your target and begin killing. if your lucky they wont even focus you.

to be honest i dont have a full rune page. i would go with flat health quintescences for early game, magic pen and flat ap runes for everything else. energy runes are not worth it. you basically dont have to worry about energy problems unless your opponents fight you 1v1 several times in a row rather than going for the gank.
i have discovered now that the cd per level glyphs are better for late game than are the flat ap glyphs, so you can grab them (-1.8% cd at lvl 18) instead if you find that you die/miss kills because of cd too long at end game if you dont get deathfires because situations dont call for it/require something else

i go 9-21-0 because it gets you some extra magic pen, which is always good, and some cd, important because you dont really have to worry about your energy, since its got 5energy/sec regen. also, the bonus health from defense is amazing early game, as is the 4% reduced damage. you just need some survivability on kennen, not really more damage.

alternatively, 0-21-9 also works, since ghost and teleport are hugely important on kennen, and who couldnt use some extra experience gain?

i use ghost and teleport. i cant really imagine using anything else on him. you MUST be there for team fights, because your CC and AoE casts will turn team fights like nothing else. people tend to panic when they get stunned a couple times and their health drops from your burst damage.
aside from those, you could put exhaust on kennen, or clairvoyance since kennen is an amazing mid. i cant think of anything else you could put on him, unless its rally to boost team fights some.

always start with thundering shuriken (TS), then either lighning rush (LR) or electical surge (ES) if your doing well with TS then LR, because it will let you run around behind your target and get the kill that way, if not, ES is good for harassment, because you can drop it after hitting with TS for more damage. your third skill will be whichever you dont have. after that you boost TS and ES until level 3. the idea is that LR should be one level below those two, although obviously TS will occasionally be 2 levels up.

Pros
- nobody takes towers from kennen. i have defended 5v1 on towers
- CC entire teams. just remember to ult, then ES
- great harassment
- AoE casting
- can escape almost anything with LR, ghosting if necessary
- mage that doesnt have to worry about mana early game
- amazing carry (imagine stunning both ppl in 2v1 while healing and spamming ranged spells)
Cons
- squishy
- on energy, means no archangels
- can be focused
- they like to gank you

the boots early are important because kennen needs to be moving around to harass with his skill shot. with three health pots, you should be able to stay in your lane till you are lvl 8-9. your second item will depend on how its been going so far. if its going well (you've been above 50% health all game) then get mejais. the stacks come easy because of your AoE casts, you pick up stacks like crazy during team fights. if the other mid has been treating you roughly and you clearly are not in control of the lane, get hextech revolver. this gets you a lot of health thanks to AoE. LR through the minion waves, then ES and youll find yourself with health back. remember to spam TS. its a short cd and you dont have to worry about energy mostly. if you got hextech revolver, finish it to the will of the ancients (WotA). if you got mejais second, then get WotA next. it gives you much needed survivability for late game. then you get rabadons deathcap. about now you should find yourself with 500-600AP, and team fights are pretty common. BE THERE. always get to a teamfight. get those mejais stacks, get those aces. triple kills are not uncommon, and in a 5v5 you should get 6-7 stacks if they are aced. thats your core, sorcerers boots, mejais, WotA, and rabadons. now you will get situational items. your 5th item is going to be rylais if you are dying/losing kills to runners, deathfires grasp if they have a pesky tank (with 600-700ap its gonna be 50-55% of their health. remember, this also counts for magic damage, which heals you), or void staff if you just want to kill faster. the 6th item is one of the remaining 2 items, same reasoning behind them all.

if you dont understand spellvamp, let me explain. if were to cast all your spells, with a meager 600ap after full build, which is pretty much no stacks on mejais, and hit all 5 of them with LR and ES, that will be 10(210+(.4*600))*.3=1350 hp from ult 5(245+(.55*600))*.3= 862.5 hp from LR, 5(185+(.55*600))*.3=772.5hp from ES, and (235+(.66*600))*.3=190.5 hp from TS. added up your looking at 1350+862.5+772.5+190.5=3175.5hp from a full burst cast. (also, that means you burst for about 10k magic dmg) now, obviously that will never happen, since that assumes 0 magic res from all your targets. however, if you assume 66% reduced damage, which is somewhere around 100-120magic res on all of the enemies, (also never gonna happen. squishies dont have that kind of res) thats still 1000hp to you, and about 3000dmg to the opposing team, plus a full team stun. obviously they are all upset, ur teams happy (also WotA gives an aura that boosts your teams ap by 30 and gives 30% spellvamp), and this makes it pretty likely that you survive this fight, and most of their team is dead.