Tutorials on how to make new glass?

I've got a resin model of an E30 M3 that was redone to correct the horrible proportions on it and need a tutorial on how to make new glass to fit it. Any help is appreciated!

Here is a thread with a tutorial from top notch builder Bill Geary.

http://www.modelcarsmag.com/forums/index.php?showtopic=13100&hl=%2Bmaking+%2Bwindows&fromsearch=1

Thanks thats perfect