If it will be indoors, what kind of "elements" do you expect to
have to resist? Does it need to be fireproof? Earthquake resistant?
How structurally sound does it have to be? How big?

If it's going to be inside, it sounds like aluminum would work fine.
The cap of the Washington Monument seems to do ok, and it's exposed.

James wrote:
What commonly available alloy has the best corrorsion resistance
properties?

I am building a chamber that needs to last 500 years. It will be
indoors, but I need it to resist the effects of time and the elements.
I added commonly because I cannot afford some rare exotic metal.