You can find the construction details and STL files in my Mostly 3D Printed Rocker Switch Instructable so I won't repeat them here.
Not much more to add that I haven't already covered in my Mostly 3D Printed Push Button post except to say that for some reason I had a harder time with this build than the others. Maybe because of the number of magnets I ended up using, it was harder to position the reed switch so as not to be triggered by the "feedback stop" magnets. I'm thinking it took about seven iterations to get it right, but in the end I'm pretty happy with the result. Have a look (and a listen):
With a workable and customizable rocker switch in my tool kit now, I'm looking at you PDP-8/I ;-)