Step 1: Design
I recommend building an octagon-shaped wheel.
The two most important parts to consider are the width and the radius.
A larger machine is more impressive than a smaller one, but has to run slower.
Choose some elements which can be used from any angle, such as the Flipper, a Ferris wheel, or an Arm drop.
Also, keep in mind that the machine will inconsistently rotate.
Step 2: Returning Ball to Top
Use hook-shaped paths the bring the ball to the top.
Step 3: Stand
The machine needs to be held above the ground.
Attach a motor and gear to the stand.
Step 4: Counterweights and Gears
Distribute the weight of this machine evenly around the outside. The centre of gravity should be the centre of the machine.
Use gears to slow down the machine. This puts less stress on the motor.