I used a plastic coated hardware cloth that I bought on line. What I read was with hookbills that tend to chew, regular hardware cloth could pose a problem but that with softbills like finches it shouldn't be a problem.
I have an outdoor aviary in Washington state with societies and zebras. Everything guineafowling said was right on! I have a flat panel heater set to come on at dusk and off at dawn all winter and wrapped the exposed sides with plastic. The biggest problem I have had is mice! A Cooper's hawk...