Many people keep their ferrets in a cage or very well-ferretproofed
[5.1] room whenever they can't be supervised.  This drastically
reduces the risks of digestive-tract blockages from swallowing
indigestible objects [11.1], injury, and escape.  However, even if
you plan to let your ferrets have the run of the house at all times,
you'll want a cage at first for litter-training [7.2] and other kinds
of training [7.1] as well as for temporary use.

A metal mesh cage is probably the best choice.  Many pet stores keep
ferrets in aquarium-like enclosures, but they are not recommended as
cages.  They don't provide enough ventilation at the bottom, and your
ferret will feel isolated from whatever's going on in the room.  Most
aquaria also aren't nearly big enough.  Plain wood cages aren't
recommended because the wood soaks up urine and other liquids, so
getting the smell out and getting the cage really clean are nearly
impossible.  If you use wood, cover the floors with linoleum squares
or coat the whole thing with polyurethane.

If you plan to keep your ferret caged whenever you're not home, and
you'll be gone most of the day, a generous cage size is about 2 X 3
feet and 2 feet high (60 X 100 X 60 cm).  A second or third ferret
could share that size cage.  Of course, a nice, big "condo" is even
better, especially with lots of levels and hammocks to prevent falls
from the top shelf.  If you'll only be using the cage temporarily,
such as when you're vacuuming or taking your pet on a vacation [8.8],
1 X 2 X 1 feet (30 X 60 X 30 cm) is sufficient for one or two ferrets,
perhaps three.  For trips around town [8.8], a shoulder or duffel bag
equipped with a litter pan and mesh window works well.

One option is to make the cage yourself.  It may be cheaper than a
store-bought cage, and you can get exactly the size and configuration
you want.   Of course, pet stores and catalogs have lots of cages, too.
Multiple-level "cat condos" are probably the most popular store-bought
cages.  Some people like the easily cleaned medium or large size
plastic dog kennels, modified to make multiple levels, although others
think that they don't provide enough ventilation or contact with the
outside world.

Many of the condos for sale in pet stores are made by Midwest and are
available for less from Dog Outfitters (cheaper than Ferret
Outfitters).  Call 1-800-FOR-DOGS.  Safeguard will make custom cages
to your design, and also sells several standard cages.  You can call
them at 1-800-433-1819.  Sorry, I don't have numbers for international
callers.  (This is not intended as an advertisement.  Specific
products are mentioned here only because people keep asking about
them.)

In the cage, you'll want some sort of "bedroom" for your pet.  A
ferret won't be very happy sleeping on the open floor of a cage, even
on (or, more likely, under) a towel or shirt, but any small cardboard
box or basket works well as a bedroom.  Old T-shirts and sweatshirts
make excellent bedding, as long as they aren't too easily chewed to
bits.  Old towels usually work well too, though some ferrets tend to
get their nails caught in the loops.  Don't use wood shavings [6.5].
The bottom of the cage can be covered with linoleum squares, carpet
samples, or cloth cage pads.

Other than food, water, a litter pan, bedding, and a bedroom, what you
put in your ferret's cage is largely up to you.  Enough room to
stretch and move around is important, and different levels, ramps,
tunnels made from dryer hose or black drainage pipe, and so on will
probably be appreciated.  Hammocks made from old jeans or shirts and a
set of metal eyelets are very popular for both napping and playing.
Most ferrets get bored easily when caged and sleep much of the time,
so they probably won't get a whole lot of use out of toys; they'd
really rather be out playing.  Just be sure nothing you put in your
ferret's cage could hurt him, whether by catching a toe, being
swallowed, or some other way.

Also be sure your cage door fastens securely, perhaps even with a
small lock, because ferrets can be very determined and rather
intelligent escape artists.  Twist ties, cable ties, or bits of wire
often work well for fastening down litter pans or some bowls; and
clothespins and small bungee cords can be enormously handy for holding
all kinds of things down, up, or closed.