I was thinking along the same lines, and being 6'2" - 225lbs, I went with a 5" bathtub floor and put in some fiberglass rods (form an old kite) to hold them up with some tie out loops. I first dipped the ends in plasti-dip to make them more blunt so they won't tear through the fabric. Maybe it's overkill but it's still a fun project.
My floor is rectangular - 30" x 84".
I drew it up in Solidworks as a sheet metal part so I can make flat patterns for cutting the fabric. It may not be perfect, but should be close enough... It's still under construction, but I'll post back whenever I get it done.