When I lived at St Georges Road in Southwark in the sixties we-the-guys had an idea to build a false level into the lounge space as this was a terrace property famed in London for the social aspects in architecture the ceiling height was a mear 15 feet high allows for such moderniziums.
So when I saw this kit at Gizmodo that has many dimensions might have aided the construction but then you have to grasp the aspect of several mad~drunken people jumping up-and down on it

link to DIY Projects page