My own birdrooms are ten feet high at the roof apex. This I feel gives plenty of ventilation which reduces incidences of dead in shell and also allows the use of all wall areas, with the exception of the door space. This allows me to keep the temperature at a reasonable level with just a one kilowatt fan heater, thermostatically controlled, throughout the colder winter months, when the birds are breeding. The wall surfaces can be easily washed down. Flight areas, both inside and out, are in my opinion, essential to maintain fit active Budgerigars throughout their lives, from barhead to adult.
Flights prevent the build up of excess body fat, particularly in hens.
In providing flying areas certain rules should be adhered to. Ensure that both inside and outside flights have sufficient space to accommodate the number of birds you can expect to produce. Overcrowding can easily lead to outbreaks of disease. Vary the perch size and level to ensure adequate exercise for feet and wings. Cages vary in size and design but I consider that stock cages of good size are essential for housing barheads on weaning, for show preparation and for sale birds.