In general, the larger and the more active the bird, the larger the bird cage should be. The amount of time the bird will spend in the bird cage each day is also a factor.  A bird that is caged most of the time requires far more space than a bird caged only at night.  Some birds have special requirements. Amazons prefer horizontal bars, as they like to climb. Messy eaters should have a seed skirt to catch food.  Breeding birds may require a nest or breeding box and a larger sized bird cage.  Smart birds, like parrots and crows, need secure latching mechanisms to prevent them from figuring them out, and often require toys and/or playstands to keep them entertained.  Parrots in general tend to gnaw on bird cages, with larger macaws known to tear bars from flimsy cages.  Zinc coated cages or chicken wire could cause toxicity to parrots over a number of years.  While small bird cages are relatively cheap, large, parrot-sized cages can cost hundreds or even thousands of dollars. The materials used to build the cages has a lot to do with the price level.  Most parrot cages are made or wrought iron and painted with a non-toxic paint referred to as powder-coating.  However, the newest trend in the market is cages made of solid stainless steel. Large parrot cages made of stainless steel can cost thousands of dollars and will actually outlive a powder-coated cage by 5 to 6 times. A Galah in a aviary with wide bar spacing. A bird cage for a tame pet bird which is allowed out daily should be large enough to allow it to easily extend its wings fully without hitting cage sides or toys or objects within the cage. In some countries, it is illegal to house a pet bird in a cage that does not permit it to spread its wings. Wingspans of common pet birds range from approximately 12" for a budgie and 16" for a cockatiel up to as much as 36-48" for the larger macaws. Untame birds which are not allowed out of their cages regularly, such as most finches and canaries, require larger bird cages that are long enough to permit some flight. The bars should be spaced so that curious birds cannot stick their heads out of the cage and become stuck. The cage should also be made with non-toxic paint, because birds tend to gnaw at the cage, and if the paint is consumed, they can die from poisoning. Cages should also be equipped with appropriate perches. There should be several diameters of perches available.  Flight cages and aviaries should be equipped with perches at each end with open space in the middle for flight.