A model of a traffic light in openscad. To create an USB controlled traffic light for your desk, equip this with the electronics described here: https://github.com/holgero/XFD .

See it in action: http://www.youtube.com/watch?v=HyK4Re3XgTo

Adapt the sizes in the scad file to your needs and let it render one of the modules corpse(), shaft() and casing() each to stl or use the attached stl files. There is a section "if (plate)" in the scad file, if you activate that it renders the three parts on the same level (I didn't use this, after I had some trouble with the corpse and it spoiled the other parts (3 times)).

If you do not plan to use the USB control of the traffic light you might want to remove the hole for the USB plug in the casing.

Slice and print each stl file. I used 0.4 mm layer height for all three files and support only for the corpse (but this is probably not needed on most printers). Slic3r created gcode for the shaft that was only one line thick, so it didn't fit very well into the corpse (it was too loose), perhaps it works better with skeinforge.

Assemble the LEDs in the corpse and thread the wires in the shaft to the casing. Glue the corpse to the shaft (hot glue worked fine) if it is not a thight enough fit. Connect them to the controller circuit in the casing. Screw the base plate of the shaft to the casing.

I filled the corpse with hot glue (after testing that everything worked). This hides the LEDs from view and diffuses their light, looks much better now!