Tanks are all about CC and disabling, and Kennen is really good at that. I haven't bought him, but I've seen him CC whole teams.

The reason why I think tanky kennen would be cool (Rylai's, Randuin's, etc.) is because his AP ratios aren't that great, but his stun is.

Wouldn't this work out decently?

No.

I've seen high ELO streams where Kennens get Sunfire Cape....Seriously.

Tried it, not too bad. The main problem is that while he can dish out a lot of damage and can easily AoE stun, he is not capable of doing it on demand. This means that you're more of a damage sponge rather than a true tank--you can't save your team when you need to. It kinda runs counter to having a tank to begin with.

So, Kennen offtank--very doable. Kennen tank..not unless your team is very organized/has other CCers.

I found you pretty much have to get a decent amount of defensive items on kennen because to do his full damage, you really need to be in the middle of the fight.

Build for ap/hp and he works well. Rylais, mask etc

my friend plays tank kennen.
you cant really be the main tank on your team (effectively) but late game it works good because a flash ult into them is great initiation and he doesn't die instantly

yeah I've seen kennen offtank do extremely well before, but it is really better to have another also

When Kennen first came out he was more viable as a tank than an AP champ... they buffed his ratios, but he's still effective as a tank.

Rylai's is still essential for a tank build Kenne.

its not reliable enough. he can do what amumu does, but it requires some pretty slick moves before he can do it. if you've never played kennan before, its actually fairly hard to use him in the team fight phase. in order to get your stun go gotta get some good work in with your electric ball and that means you gotta be pretty close. your liable to get stunned or rooted if your trying to intitiate against a whole team.

malphite and amumu are the big aoe disrupter tanks and they both have moves to get them in close really quick without too much risk of getting shut down. The other tanks are more taunt or shield oriented so they are kinda a different sort of tank. however, off tanking with him is great cause if your enemy is focusing on your tank, or even your carries, its unlikely they are gonna be fast enough to take the time to shut down a blur of electricity.