Floor 304 was the top floor of Paradise Towers. No one was allowed access to it under pain of death.
Floor 304 was kept clean due to the absence of any life there. It was maintained by cleaners, including an aquatic one in the floor's pool. It was this pool that earned it the Kang nickname: "the pool in the sky".
Upon their arrival at Paradise Towers, Melanie Bush and the Seventh Doctor designated it as their meeting place should they be separated. They were separated and Mel had to make her own way there. Together with Pex she took a lift up to the floor. Pex was agitated by how clean it was. Mel took the opportunity to relax and swim. In the water, she was attacked by the aquatic cleaner. She made it to the shallows and used Pex's gun to destroy it.
The Doctor joined her, along with the Kangs. Kroagnon ordered the cleaners to gas all the floors starting at the bottom and working upwards. Many of the residents were forced to Floor 304 including the Rezzies and the Caretakers. They formed an alliance and left the floor when they moved to attack Kroagnon. (TV: Paradise Towers)