Tell it the cardboard you have and it lays out a tilt-maze: one path from start to exit, with hazard holes on the wrong turns. Tilt the tray to roll the marble to the exit without dropping it.
Wider corridors are easier and leave room to steer past holes you drop in the path; a finer, denser maze is meaner. Scrub the seed or hit Shuffle for a new layout, then download the SVG to lay out your build.