4 x 12 feet is huge! Aviaries are a good place for reasonably compatible species because it gives the birds plenty of room to get away from any individual who's being obnoxious. Budgies and Bourkes are both Australian grass parakeets and the natural habitat of the Bourkes is smack in the middle of budgie territory. So they encounter each other in the wild, and should get along pretty well in a nice big aviary.

yeah I know it's 12ft long because that is how long our bedroom is. It's pretty close to 4 ft wide and I just used netting I had lying around for both sides of it and I put strips of tape on the netting so my budgies could see the netting because I don't want them flying into it lol. I know a guy who runs a greenhouse here where I live and bought some plants he said would be safe for them. It also goes from floor to ceiling which I believe is 8ft. So for like $50 bucks my budgies have a 4x12x8 ft aviary.