Hi Tim,
unfortunately no matter how good your DIY reflector may be, the time and effort spend don't worth it, because there are many available reflectors from aquatic (and not only) companies that offer good products on good prices...
Inspite the above, if you want to try your skills there is a good article here! I believe that the guy may exaggerate a little bit, but there is good info inside!
Friendly,
Giorgos