good on you mate dont listen to em building massive cages is good fun i had a cage that size when i was 16 for a 11ft coastal. i would suggest doing a mixed zoo tank like maybe central blueies and beardies with heaps of logs rocks and fake plants ect good luck whit it and keep us updated.... only down side i found was haveing to take it apart to getit out doors
go to old building supply yards and buy second hand alli window frames 2400x 1200 is a fairly comon size and then the doors are already made