Today i got the answer from the lady at the building inspection office.
In our state its not possible to build an aviary like mine without a planning and building permission.
So I answered and asked the lady if there is any kind of aviary I could build, maybe smaller or combined with our house, or an altered caravan. Because I want to have a habitat for the budgies that is as natural/animal friendly as possible. I really hope she has good news.