Wild quail live in brush. They prefer to simply hunker down somewhere at night, rather than roost like chickens do. You could give them a small box or two to hide in, like a mini doghouse, but they may never use it. Mostly what they'd be happy with would be a big pile of straw to hide in, or a fake bush. Christmas tree branches (fake or real) are ideal for that.
An aviary style sounds great to me. Just make it deep-litter, and you should have happy birds. If I were you, I might try to make it wider than 3 feet? It'll be kind of cramped for you otherwise.
Trouble is, 7 by 3 is 21 square feet. For 20 quail, you'd want something like 40 square feet. A little under might be fine, but you want something at least approaching 2 square feet per quail for happy birds.