Kenneth, your design will have to start with the bearings used. Most town will have specialty places that deal in casters. Seeing what they might have "cheap" will be a good place to start.
There are a lot of things that you might use, but I think that industrial casters, the kind that will hold 40-400 pounds per unit should be enough. You will want enough casters to hold at least twice the expected load.
The next issue will be how to locate them. The caster, of course, will be attached to either the floor or floor substitute and the revolving disk should have a track for the bearings to run in. You might be able to find someone to roll form 8 foot lengths of extruded aluminum angle or channel. You will need about 30 feet.
Those 2 parts will be the major design factors. I would think about using the 3/4" thick sheets of plywood with tongue and groove edges for the moveable disk.