Plop just tells you where you should place your support points for optimum mirror deformation (within the thin plate approximation). But you don't really need the program, because the results for most common scenarios have been tabulated. Just look it up here:
http://www.atmsite.org/contrib/Holm/...lls/index.html
Also check out Toshimi Taki's wesite (plop principal author):
http://www.asahi-net.or.jp/~zs3t-tk/
There appears to be as many ways to make a mirror cell as there are amateur telescope builders. Most books on telescope making will have something to say about mirror cell construction. You can find ATM books in most of the bigger libraries, or you can buy them from astro dealers like Bintel.
Good luck with the project!
