I just got a couple of ferrets last week, and to accomodate them, I got them a 58-inch tall cage with 4 levels for them to climb and play. Naturally, the bottom level has a nice, deep pan for litter. Naturally, they prefer to play in the litter and do their business on the third level. The thrid level
consists
of a hard plastic floor, with a shallow gutter around the edge to collect spilled water or urine. The problem is this: The floors are perfectly flat, so spilled fluids (like water and urine) tend to pool in the middle of them, requiring frequent scrubbing and frequent bathing for the ferrets, whose fur gets soaked in it. While I could always tilt the floor slightly, that would cause all spilled fluids to collect in only the lower portion of the gutter, which can only hold so much.
Poo isn't much of a problem, because they do that in the corner, against the bars, and the big one even figured out that he can reduce poo buildup and be more hygienic by kicking it out of the cage, where it lands on the newspapers I placed on the floor around the bottom. Very convenient, and I couldn't be prouder to have such a clever pet.
What I have not seen in any small animal cage, and what I am proposing here, is upper floors with a very slightly slightly raised center, like a pyramid, with a gutter around the edges that has tooth and claw-proof drain tubes, just like the ones on houses, that run down the side of the cage and empty into a removeable pan in the bottom of the cage, below the litter pan. This way, they can play in their sandbox, do their business on whatever floor they choose, and it doesn't stay up there, requiring constant scrubbing of the floors and constant bathing of the occupants.