I used half- inch mesh for the fronts of my indoor quail cages, mainly because it was left over from the chicken run, but it does have the advantage that they are protected from small predators such as mice and weasels. ATM mine are in a rabbit run with wire mesh about 1.5 cms by 3 cms I suppose and this is fine. If you keep coturnix quail (Japanese or Italian) as adults they are quite large birds and larger mesh would contain them, but of course if you want to keep Chinese painted they are much smaller. As youngsters there would be a week or two once they were out of the brooder when you'd need to keep an eye on things, but then you could temporarily block off the mesh I suppose until they grew. They are adult at 8 weeks, a lot easier than chickens!