Sure, you could just buy a conventional hula hoop at the mall, but for a colorful, durable hoop with a customized fit, it's better (and more fun) to make your own.
Soften one end of the tubing by soaking it in very hot tap water for two minutes.
Slide the heated end of the tubing over the coupling until it reaches the midpoint line.
Soak the other end of the tubing in the hot water. Before the tubing cools, use a funnel to quickly pour the plastic beads into the coupling-end of the tubing.
Immediately slide the bare end of the tubing onto the coupling so that the two ends meet.
Wrap the seam with a couple of layers of colored tape to seal it. Decorate your hoop by wrapping it with contrasting colors of tape. Wrap each color at a different angle for a woven look.