6 feet minimum height. 7 feet if you can do it. My ceilings were all 6 ft. Only one time in all my years of keeping them in aviaries did one hen flush up this high and break her neck. Something came prowling at night. The quail do enjoy doing laps around the aviary and normally don't fly this high however. You can put in a false ceiling with a net or something that hangs down just in case somebody does flush.
I also use solar lighting all around the outside of the aviary, coops and runs. Like an airport run way. LOL But it really helps to repel the night critters. Predators are really drawn to quail and will come for miles when they smell them. I used railroad ties and buried one completely, then another on top to attach the panels too. Make sure your facilities are predator proof as possible. If you feel safe sleeping in there, then your quail will be safe as well.