Unless you are going to go and get stainless steel parts made up or pay for powder-coating, you are pretty well stuck with timber and as AP said, your Cockatoo will most likely eat his way out lol. I recommend buying a good quality cage, even though they may be expensive, in the long run they will last longer and give you less of a headache in assembly. Plus if you buy a good one, you can be sure the materials are safe.