Spiral phase plate looking for advise on making shape..tia sal

Greetings all
I'm trying to make a spiral phase plate out of plastic (see link below). I have all the tools I'm just a little lost as
how I should procede. It doesn't have to be perfect or large. The Diameter would be just 5 inches

TIA
http://www.st-andrews.ac.uk/~www_pa/...ents/spir.html