This is a little off topic, but does anyone else feel like you shouldn't call something an aviary if you can't walk inside it and stretch out your arms?
When I think of an aviary, I am thinking of something room-sized, not cage-sized. A building or large enclosure that you can go inside at the same time as your birds. For a big cage, I prefer to say "flight cage", since it is a cage, but big enough to allow for short flights.
Of course, I have also seen the term "flight cage" used to describe some really tiny cages, so I suppose there is not much standardization regarding how these words are used.
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Back on topic, are you looking for an indoor or outdoor aviary? What is the maximum size that will fit in your available space? Any other features you would like to have? What is the biggest bird that you plan on putting in the aviary? How about the smallest? That will be important for wire spacing and guage. Have you considered building your own enclosure?