The way The End is handled is there are two final worlds.
1) The main world is called The End, and each time the Ender Dragon has been killed this world and the dragon will fully regenerate and respawn every 1 hour, as to allow everyone a chance to kill the dragon.
Also, once you have defeated the dragon, feel free to spawn a Wither in The End as the world will be fully restored later.
2) The secondary world is called Thee End and this world does not have a dragon so you are free to build. After you have defeated a Dragon, you will be allowed access to the second world using /warp thee_end
Players that have so far managed to kill an Ender Dragon: