The damage Dealer is meant to be Fast , also its more like hit and run , and if you got the enemy Down to around 20% even the normal DMG is high .

For the build you need a Huge amount of Money so you need a Team wich tolerates the Farming .

Becoz of the Low HP and Armor dont try to be a Hero and go alone .

Early Game
When the Game starts you need a Quick hand for the Skills , kennen already got a Good DMG at the start of the Game so you can easily make the First Blood even against tanks .

Mid Game
After reaching lvl 6 or Higher dont overestimate youself becoz you got the Ultimate , duo to the fact that you wont will have such a high amount of money your dmg will just hurt a bit , but there comes the hit and Run , use the Shuriken to hit the enemy Untill you have him below 60& Health than go and give him everything you got .

Late Game
From 15-18 you already got great items but still dont overestimate youself by going against the enemy Team alone , the Enemy will have great items as well as you so always stay with one of your team . In the Late game Kennen will be an FF target so concentrate on the support , you will see that you will have more Assists as kills and deaths together .

Pro
High Magic DMG and Physical DMG
Can solo Nearly every Mage or Champions with lower HP as youself and without Heal

Con
Needs much Money
Needs to be able to move

If you go to Push threw one Line (Mostly Middle) and got the whole Team with you be prepared for the enemy , Kennen can deal high DMG over a short time but against the whole enemy team it is hard to stay alive for the time . Always try to stay in the crowd becoz enemys know about kennens DMG soon so they will aim for you .

At the Beginning the Shuriken is your best Choice to quickly deal DMG .
Later the shuriken will be your 3rd attack to stun the Enemy and kill him with the ultimate.

the full was of Usage will be : Lightning Rush - Electrical Surge - Thundering Shuriken - Slicing Maelstrom .

Mostly this combination requires that you have heal with you , most enemys Decide to not run away after you stunned them and thats there Death , the Cooldown of Kennens skills is later around 5 Seconds so you can nearly spam them !

Some enemys will run when you use Lightning Rush so try to Lure them close enough to give them all your Skills .

My DMG Dealer build is hard to play , the Build is concentrating on the early and Mid Game becoz at the Late game your there to support .

The build itself works fine for me the only Prroblem is that im just lvl 15 , but out of 6 games i won 4 with the already Mentioned Assist stats above the kills and deaths , i just once reached a 27/8/12 , but that had to do with the enemy Team wich was mostly made out of mages wich obviously cant take all the dmg kennen deals .

But i hope this build will be Helpfull for you .

Please leave me a comment about how i could improve , its my First Build here so its kinda hrd for me to do one XD !