somthing like that, i used a 24 inch one, it wasnt big enough to lift me i was like 140 lbs, try a 3-4 footer.
get a peice of ply wood, and seal up one side of the donut tubing. it has to be air tight. drill a a hole, use a gas power air blower, the air blower will cause a skirt of air under the tubing/ hovercraft to be lifted off the ground.
the hard part is getting a fan strong enough to propel you.