We have 5 ferrets (1 male 4 female) and a Ferret Nation cage that's 3 high - it reaches almost to the ceiling! I'd been searching for litter pans that made sense for this cage. I've tried the pans made for ferrets, rabbits, even assorted sized cat litter pans and nothing seemed to really fit well enough to encourage them to use the box and also keep them from moving around.
What I found to be nearly perfect are Sterilite 28 quart storage boxes. I picked them up at Walmart for under $5 a piece.
I have two in the bottom level, which nearly fills the entire space. I also have one under the half shelves in the upper two sections.
The sides are nearly the perfect height - the ferrets can easily jump over the sides to get in and out, yet they're just high enough that they've never managed to back up and get it over the edge.
I've also affixed coroplast sheets to the sides of the cage with zip ties (aka cable ties) to prevent them from making messes that spill out to the floor. I made these pieces to fit the sides in length and they're about 7-8" tall. The zip ties keep them from being relocated.
I use the compressed wood pellets as litter.
I also located their food and water dishes on the smaller level shelves, and it seems to have put a halt to them going in those corners.
On the 3rd tier, I have a bin with a hole in the lid which contains starch packing peanuts as well as a 4th litter box.
I've found I have the best luck scooping waste out of the boxes at least every other day, but with this set up they can actually go a week before any real smell is noticeable. I discovered this during a VERY busy week!
I also particularly LOVE the plastic quick lock crocks for food and water. I have two 20oz for food and another 2 for water. Food is filled as needed and the water is refilled at least every other day if not daily. The ferrets cannot move these around!
To cover the floor pans, I bought some cheap (as in under $5 each) fleece blankets and cut them to make covers for the cage floor trays. These were simply cut and sewn while ON the tray to assure a tight fit. They slip on and off easily to wash. I have two sets plus a back up so there's always a clean set.
Finally, I don't use all the ramps that came with the cage. I use the one that is for going in and out of the cage during play time and then I use the ones that go between tiers. I do NOT use the ones that go from the half shelves to the full shelves. When the half shelf is placed in the middle, our ferrets can easily jump/climb up and down. Half the time they were doing this anyway, so it seemed reasonable to remove them and see how they did.