In the past few years, we have covered a bunch of awesome marble machines here. This 3D Printed Triple Marble Machine is also worth a look. It comes with interchangeable modules, so you can watch the marbles go around the track all day.
The set comes with 50x marbles. It measures 17.7″ long, 7.9″ wide, and 8″ high. This marble machine is 3D printed in PLA.