An all metal non-coated cage is the best choice for your bird. He will chew on the bars as that is part of his play and general lifestyle. A metal cage is easier to keep clean and prohibit infestation of pests.
Insects can hide underneath coatings and inside the wooden bars.
Inspect the cage to make sure he cannot place his head between the bars. Size of the cage depends on how large or small the bird, and how many you plan to house in each one. Each one must have sufficient room to stretch out and move around. A slide-out drawer bottom works better than one you have to dismantle the cage to clean out where he has messed. Cover the bottom with newspaper, sand or other similar materials to absorb urine and feces.