A removable base tray will make cleaning so much easier. Avoid cages with plastic trays, as these are easily broken and not replaceable. Suitable bars or mesh for your species of bird is vital. The width and gauge of the wire will depend on the bird, so research this aspect. Make sure that any cage you purchase with welded mesh or bars is thoroughly cleaned and scrubbed with vinegar and sun dried before use to avoid heavy metal poisoning in your bird.
Castor wheels are a great asset if the cage is large.
A sturdy stand that will not be easily toppled is also beneficial. Your parrot's cage height should come to around your eye level or just below. The cage should never be placed on the floor or low down in its designated room, as this may lead to stress in your bird. The doors and openings should be of an adequate size to not only allow your bird in and out but also to assist with cleaning and daily changing of food and water bowls. A rooftop play area is a great addition but such cages are a little hard to find here in Australia so you may have to provide an additional stand or play gym.