There are many different ways to house ferrets, and everyone will have their own preferences. My major advice is to give ferrets as much space as possible!
Many people who own a lot of ferrets house them in tiered outdoor hutches. Unless they are large custom hutches (at least 6ft x 2ft x 2ft), this does not allow enough space for ferrets to run and play, and it is hard to provide enough stimulation a small enclosure to keep ferrets happy.
It is common to house ferrets in large cages indoors, which ensures ferrets are sheltered from the elements, and often have more interaction with their owners as their cage is passed many times a day. Be aware that ferrets do not cope well with heat, and central heating can often be too warm for ferrets in the winter. The unnatural daylight hours indoors can cause ferrets to come into season at odd times, and even if neutered, could contribute to the development of adrenal gland disease. A good compromise here is housing ferrets in a garage with a large window for natural light, where they are unlikely to be overheated in the winter, and it is easier to match the natural daylight hours.
I do, from time to time, house ferrets indoors if they require a little extra TLC or if I need to watch them closely. I use various multi-tiered cages marketed for rats, rabbits or ferrets, but it is important to ensure the bars aren't spaced too far apart, as miniature ferrets can easily squeeze through the bars on cages marketed for rabbits!
As ferrets are easily litter-trained and are naturally very clean animals, it is possible to allow ferrets to free-range in the
house, and just go into a cage at night or when unsupervised.
It is very important that you 'ferret-proof' your home. Ferrets will steal and stash most things, they may decide to chew wires, they especially love rubber, and will try to chew up and eat rubber objects which can cause intestinal obstructions and be life-threatening in ferrets. Ferrets can escape through surprisingly small holes, so it is important to ensure that all small gaps are blocked up so that you don't lose your ferret through them!
Ferret courts are ideal for housing ferrets; big outdoor enclosures, with a roofed aviary-type area with logs, soil and tunnels. This allows ferrets to express many of their natural behaviours and means that if one day you are too busy to let your ferrets out for a run around, then they will still be able to adequately exercise. If you house your ferrets in this way, they must have an insulated and sheltered area to sleep in.
I personally house my ferrets in a mixture of different enclosures, I have a custom-made 10ft x 6ft shed, fully insulated and lined with plastic stockboard
for ease of cleaning, and separated into one 2.5ft x 6ft enclosure, with 3 tiers on one side, and another 3.5ft x 6ft enclosure with 3 tiers on the other side.
I have the option of splitting these into separate tiers (for raising litters) or joining all of the tiers together to allow a bigger group to have more space.
I also have multi-tiered hutches, with tiers joined to the others using tubing, and several 'mini-court' type pens, which I usually join together with tubing to allow the ferrets more space.
It is important to provide plenty of stimulation for ferrets. Mine have hammocks, cat beds, tubing, deep cardboard or paper bedding to burrow and dig in, and plenty of tinkle balls and soft toys which they thoroughly enjoy playing with. They also have an ample number of litter trays with wood pellets and cardboard squares as litter, this keeps the main pen very clean and makes clean out day a breeze! It is imperative that your ferret can fit all four paws in the litter tray otherwise they may reject it. Some rabbit litter trays are ideal, I tend to use big storage boxes and cut out dropped entry-ways using a hot knife which are cheap and easy to clean.
When out and playing in a larger area, ferrets love low cat trees to play on and climb up, ball pits to bounce through and burrow in, digging boxes (or sandpits!) and even thoroughly enjoy a paddling pool with an inch or two of water in the bottom! Be prepared with a towel to dry your ferrets off after though, as they will typically get absolutely drenched!
However you house your ferrets, and however much space they have, they must always have time to play and interact with people. It is much easier to deeply instil nip-training and keep up regular handling than to leave ferrets untouched for long periods and then try to rectify a biting problem later!
You can also harness train your ferrets and take them on walks. I would recommend a Canine Distemper Vaccine if you intend to walk your ferrets, even if only in your own garden. Ensure that any harness is very snugly fitting - hamster figure-of-eight harnesses can be ideal for the smaller ferret!