What are you wanting to build? A Drum kit? those are the 2 most common woods used for drums. Most people who have sagging issues with melamine are because they have had the rack for years, not just one year. Anything will wear over time, that's a given, but Melamine is a great option because it doesn't have any odor to it, it lasts a long time. I think your discrediting melamine, if you spend $200 on nice looking and well built rack that lasts 5 years, i consider that a good investment. I also notice that it is hard to find large sheets of Maple or Birch and plus to paint and seal the wood to look nice takes a while and still doesn't look as good as the smooth surface of melamine.

Plus i don't hear anyone having problems with a well made 32 qt and hatchling racks, most of the sagging is due to breeder racks and racks that weren't made well enough, or the humidity is way too high in the building, etc. Just look at your situation and see why like 80% of the reptile industry who can't afford freedom breeder racks use melamine.