Quail need a safe, sturdy area with shelter from extreme weather. Especially if you live where raccoons and other predetors are present, you will need to make sure that the enclosure of your choice is secure and predetor-proof. (raccoons can be especially crafty) A good enclousure doesn't need to be expensive, but it does need to provide the following:
You do not want raccoons, foxes, raptors, or other predetors of small animals eating your quail, their eggs, or their food. Fortunately, many options exist to prevent wildlife from interfering with your quail.
You can get fairly inexpensive latches from hardwear stores, HomeDepot, or Lowes. Raccoons shouldn't be able to open these, provided they are installed properly and are high quality. That being said, you can inforce your latches with:
I don't use these, but they are probaly a good choice to keep especially clever raccoons from getting into your quail enclosure. You will want something that won't rust or degrade from harsh weather, so stainless steel padlocks are a good option. You don't need anything fancy, but it does need to be able to hold up against weather.
It is important to provide good ventalation for the well being of your quail, but make sure that your enclosure doesn't have any gaps or openings. Animals in the weasel family, as well as some snake species, are able to squeeze into gaps even two inches wide.
This is an easy yet effective way of keeping your birds safe. Placing bricks around the base of your coop, especially if your quail have an outdoor pen, is a great way to keep your birds safe. Coyotes, foxes, weasels, raccoons, etc. can dig around the base of a pen and take multiple quail easily. Bricks placed around the entire base of the enclosure are useful in that they will discourage predetors from digging into your pen, and in addition can look nice.
Quail can be sensitive to extreme cold and heat. You will want a weather-proof roof to shelter them from rain and snow. if you are building your own enclosure, be sure to make the roof slanted: this way, rain and snow won't accumulate on the roof. If you are purchasing an enclosure, look for a slanted roof for the same reasons. I highly recommend starting with couternix quail since in my experience can be cold and heat tolorant. One of the best things you can do for your quail is provide liquid water and plenty of food in the cold, and cool ice water in the summer. In addition, healthy birds will be much better off in extreme weather than unhealthy ones.
The minimum space for quail is about 1 sq. ft/bird. If you are able to provide more space than that, I highly recommend it. Males especially can get territorial, especially spring-summer, so more space means that fights can be kept to a minimum, although you probaly will still experience some fighting. Even if you are raising quail for commercial use rather than for pets or as a hobby, quail benefit greatly from a large space to run and play in. Crowded animals of any species become unhappy, disease and sickness will spread quicker, and animals will resort to behaviours such as pecking at each others' eyes and feathers. More space is one of the things that you, as their caretaker, can provide to prevent these issues.
Whether you are making your own enclosure or purchasing one, look for a design that makes accessing and cleaning your coop easy and efficient, and that will fit your needs. For example, if you don't prefer bending over to clean a coop, a rabbit hutch design might be a good choice. Whatever enclosure you choose, it should be easy to rake out litter, move, etc.