This is a very small toy (not for young kids). This maze is designed to take four balls, with the goal of simultaneously moving all four balls from their start to end positions by tilting the maze. It also is a nice demonstration of thermally bonding a different material to PLA -- a sheet of overhead transparency material is used to make the transparent cover of the maze.
Detailed instructions are posted as an Instructable:
The images show the completed maze (with my two cents as a size reference) and the parts before assembly. The maze body is 3D printed using the SCAD or STL file given here -- these were made in PLA using a MakerGear M2. The transparent cover is cut from a sheet of overhead transparency material -- I made these with a Silhouette paper cutter following the postscript pattern in mazetops.ps. The 1.5mm diameter ball bearings are placed in the maze body and the cover is thermally bonded using an ordinary clothes iron on a fairly low setting.
Printing the maze larger, for example at about 150%, allows larger balls to be used and the balls will move much more smoothly.