Give me the choice of a cage or an aviary and I will choose the latter nine times out of ten! I know that sometimes a cage is what is needed, but I do not think you can provide a better home for your budgie than a well-designed flight.
Simply giving your bird more space to fly around is going to give it an improved quality of life. More exercise means better health and more mental stimulation, which leads to a happier budgie.
You can set up interesting play areas, provide a place to enjoy the sun or the rain, and keep more birds together in a flock. And the extra space can be enjoyed whether you are there to monitor them or not, whereas letting your bird out of its cage to exercise can only be safely done under supervision.
The main reason for containing your budgies is to keep them safe. So aviaries must be made of materials that can keep predators and pests out (including cats, dogs, birds of prey, rodents, mustelids (stoats, ferrets etc) and sometimes children!)
Cost of materials will play a part in your decision; most of mine have been made of timber frames, plywood and wire mesh. Other materials such as brick can make very nice and better insulated aviaries. Outdoor aviaries need an area where the birds can enjoy the fresh air and weather, and an area they can shelter from wind, rain, direct sunlight etc if they choose to.
Then you also need a sheltered place to put food and water, and some perches. Perches should be placed so that they allow the budgies to fly for the longest possible distance. They need to be placed in the sheltered area and out in the open area.
Once you have the basics planned you can add the fun bits!
They can be accessorised with toys and places to hang millet sprays, fresh branches with leaves and greens. A swing is always popular too.
If you live in a dry climate you can lay an irrigation hose over the top of the aviary to let it ‘rain’ occasionally. This means one end of the flight should have a netting roof rather than a solid one. My budgies used to love hanging upside down from the roof with their wings open when it rained!
I got my first one when I was fourteen years old. It was second hand and came with two pairs of budgies! It was basically a rectangle, with one end covered over, a shelf to put the feed dishes and a couple of perches at each end. Although it was a very basic aviary it did a good job and I used it for a few years until I was able to get a new bigger one with a small area for storing feed and using as a breeding area. The main problem with the small original one was how quickly I filled it up! It is tricky to stick to a couple of birds when there is space for a few more…….