I have made quite a few of these, I usually scavenge the stuffing from old pillows - this sort is often bouncy and washes well without clumping or flattening. I usually use corduroy for the outer and fleece for the inner and a PVC type fabric for the outer of the floor which seems to be a bit grippy and reasonably hard-wearing. You will probably need a sewing machine to make these, I just have a basic Bernina machine and have no trouble at all using the normal foot.
The instructions are a bit hard to follow unless you have the materials in front of you and I have made myself some patterns out of parcel paper for cutting out all the pieces, so that might be handy too.
I have about 8 of these in total now and have lost track of how many times they have been washed - the ferrets love them! You might want to make the pattern bigger for bigger groups of standard ferrets - most of my ferrets are minis so they can fit about 5 in these, but probably only would get 1-2 standard fezzas ....
Ferrets: Contessa Kitties: Watson, Oskar DIP Sinnead, Vincent, Boris, Zeus and Athena, Willow, Mr. Frodo, Indie, Lucrezia, Judge, Odin, Miss Emily, Suki, Cody, Aristotle, Butterscotch, Frankenfurter. RIP Herne, Ligeia, and Mr. Stubbs