Each Local Government Area or council area comes under its own council. You do need to get a permit and makes the plans as required; however, as long as something isn't perceived to be unsafe by others (and that's assuming that what is built is even visible to neighbours), it is probably somewhat unlikely to be reported.
There are some scoundrels around who purport to be licensed this or licensed that. (For example, unlicensed roofie caused us no end of trouble. My father trusted someone he shouldn't have trusted; he wasn't completely back to himself after 3 months in ICU. Otherwise my father would have been much more scrupulous in checking his credentials.) But mostly in Australia the tradesmen are licensed. Some are truly lovely people. We use a plumber, for instance, who is amazingly helpful and a lovely bloke. He never overcharges.)
My view is... is it safe? If so, there'd better be a very good reason for even thinking about reporting someone. Life's too short for going about looking for something to report...