Well you need to start simple to design more complicated machines.
Here are some of my starter marble machine works.
1- A simple swing which moves with the gravity
all solidworks (version 10) files are included
2- A marble and the channel it moves with the simulated gravity.
3- A marble and the helis on which it travels due to the simulated gravity force.
4- A marble and a long thin canal with curves and 360° turns in which the marble moves with the virtual gravity.