I imagine either metal will work all right, probably 0.065 aluminum tubes will support a person. Aluminum is more difficult to weld properly, and you will probably need a wider base to support a person if you use aluminum (so that they don't tip over).

The picture shows a lot of curved bars and those won't be easy to make. You might consider trying to use only straight bars. I'd suggest building a preliminary frame out of wood first and trying to sit a person in it. Shouldn't take you more than a day, and if the wood can support a person the tubes should be able to as well.

Cool idea though :thumbup: