I wouldn't suggest making a cubes cage for a ferret. Even a mesh rather than wire-grid style cubes have holes in the corners that could trap ferret legs, leading to sprains or breakage. The wire grid cubes that I've seen have holes much too big for me to feel comfortable putting a ferret in. Cubes are most often used for single story cages for guinea pigs or when used in a multilevel cage, the floors are carefully covered with carpet to prevent feet from going through. People have used carpet sample squares to cover floors, but with the way ferrets dig and rub on carpet, not to mention pooping outside the litterbox, it may be destroyed or need thorough cleaning more often than is worthwhile.
If I were you, I'd go for the PVC coated 1/4 inch square wire mesh that is sold by home depot and make a cage with that and zip ties.
http://www.weldedwiremesh.net/fabrics/pvccoatedweldedmesh.htm is approximately what it looks like.
It has been used here before to make a nice quality huge rat cage, for ferrets I'd make a pvc pipe or wooden frame to support it. Rats are a lot lighter than ferrets, and I'd worry about stability in an all mesh cage for ferrets since this mesh isn't as thick and sturdy as most wire used to make cages. Cage pans can be made from under-bed box halves (tend to be long and not very wide) or for a more square shaped cage, you can order just the pan from martins cages and use that. (
www.martinscages.com)
