Not Updated For Current Season
This section of the build is mainly to show my reasons for picking certain things. I am assuming that people who look at this know how Kennen works on at least a basic level. He's really not a hard champion to use.
I would appreciate it if you read this anyways before you downvote (if you are going to).
If you want help on Kennen, leave a comment here and I will be glad to help.
Pros / Cons
Shells out a lot of damage
If played correctly, can have consecutive stuns
Area of Effect Ultimate that can make/break a game
Amazing chasing potential
Not great single target damage
Healers can deal with him well (Which is a BIG thing)
"What summoner spells should I use?"
Well, there are a plenty of good options to pick from. Here's my opinion on them:
Ghost - I like using it, but you REALLY don't need it. You're going to want flash, and you have Lightning Rush. It's just fun to pretty much always get away if you need it.
Flash - Yes. Slicing Maelstrom + Flash positioning = win. Also good for escaping with your Lightning Rush.
Cleanse - Also good. Pick between this and Ghost most of the time. Probably this honestly. No debuffs ftw.
Heal - Meh. I would consider it. You DO have to run in there in the middle of them, but this build is made for you not having to worry too much about that.
Anything else is pretty much a no. Ignites, Teleports, Exhausts should be used by people who should be using them. If you want to be helpful, sacrifice your Cleanse/Ghost for something if your team is lacking it, but that shouldn't be the case in arranged 5s.
Offense - Can't really benefit much more from offense if you build him AP. Last half of the tree is mainly for AD
Defense - This is what you want. Survivability to the max
Utiliy - You don't use mana, so most of this is a COMPLETE waste.
Why This Item?
Doran's Shield - Early game survivbility. This is optional. If you solo top/mid, then I think this should be your 100% pick.
Mercury's Treads - Why not? Less CC + Magic Resistance. You have to be up in their ***es, so the CC reduction is perfect.
Mejai's Soulstealer - This one is interesting. You shouldn't get this if you don't feel like you're going to do good enough. If you buy it, and then regret it, sell it ASAP. If you don't want this, grab Haunting Guise.
Abyssal Scepter - AP/MR plus the fact that you're in the middle of ALL OF THEM, so why not give them a debuff? You might want to ask someone else if they're getting it. if someone else has it, you should get a Rylai's Crystal Scepter.
Guardian Angel - Resistances, plus that sweet unique active that brings you back to live. My favorite thing to do with this: I get hurt a good bit, but my team still needs me, go in, ult, get focused, "die", they all get owned in my ult. (hint: Your ult stays on while you're coming back to life.)
Rabadon's Deathcap - MOAR AP FTWWWWWWW
Randuin's Omen - Again, an interesting one. This also has to deal with the fact that you're supposed to be in the middle of all of them. You can slow their movement/attack speed while you do so. Plus survivability. You might want to warn the tank, or ask him if he's getting it. If the tank really wants it, get a Sunfire Cape.