There are two main special features of a floorless room. First, and most obviously, there's no "floor" or "ground" object among the room parts. We accomplish this by simply subtracting out any object of class Floor from the room parts list inherited from the combined base room class.
Second, there's no place to put anything down, so objects dropped here either disappear from the game or are transported to another location (the room at the bottom of the chasm, for example).
Floorless : object
NOTE - if you combine Floorless with a base Room class that has a dynamic room parts list, you'll need to override this to calculate the subset dynamically on each invocation.