The parrot cage is too small. What should I do if the incubator is placed outside? By the way, how about plastic? )

Plastic is ok, but I personally suggest using wood. Because wood has a good warm-keeping effect, it plays a hidden role and is opaque, which is more suitable for budgerigars. If you want to insert it, you'd better cut a hole as big as the hole with scissors and vice, and then fix the incubator with wire or something.