I have experience with poultry. I would call it vast. it looks to me that the strain of coturnix that you are using is of egyptian descent; this is a pretty hardy bunch-o-quail. Your main problem with an outdoor aviary will be rats and damp, in that order. The basic aviary for your 2:6 flock should be about 20 feet. However, these are non-fliers*, so each level only needs to be 18 inches or so. This means that you can stack levels, two or three high with ramps, and these heavy-bodied birds will use the upper levels just like another piece of ground. You can also skimp and make something like a 3X5 if you're pinched for space and they get plenty of food. Basic construction-should be fairly sturdy to keep out cats and branches. Your biggest construction problemis the roof. As I said, coturnix are sensitive to damp. While most chiken coops can have a leak or five, and can get cold and humid, coturnix cannot. They have a different type of feather oil that causes water to collect on their bodies and turn into scraggly bits of chilled bird. You should use a peaked roof that is completely watertight. Also, keep water absorbers such as hay or mildew remover in the coop so that the air stays nice and dry. You can also invest in a space heater if you notice any dampness. The heater will help your quail dry off a little faster. Second worry is rats. Coturnix are fat and slow, for birds. Rats love them, especially chicks. And, if you have garter or rat snakes, they might eat chicks or juveniles. Your best bet is to use fine mesh and to bury it at least 10" deep or as far as you can go. If you want to get fancy, you can pour cement. If you have any questions for me, I welcome them, but the people reading this post are probably bored enough already, so PM me.