Wow that sounds like a brilliant size for the aviary. Your plan seems excellent to me - no traipsing up and down the garden to visit the birds or anything, and you'll all feel close together. In terms of materials, Rosemead do very good metal metal panels but wood - if it's strong and thick enough - could also be fine as long as it is protected on the inside surfaces (with metal strips, mesh or other pieces of wood that you don't mind getting chewed). I do agree that appearance is important! In terms of height, the more the merrier in my opinion, as the birds love being high up and don't use the lower part of the aviary all that much. Anyway, I'm sure you know all this! I agree that Roz has a splendid example - judging by the photos the it both looks excellent to the human eye and is perfect for the parrots.