Carol: I don't know if you found anything yet, but you might check with
www.sailrite.com for either a PDF document or a DVD on ;measuring and making a winter cover.
I have a mast-down canvas cover for my Cal 30 and, let me assure you, a custom cover for your boat makes setting up for winter storage super easy. I had thought about making a mast up for my boat, but found that pulling the stick was pretry easy and using it as a ridgepole made it easy for me to cover the boat, by myself, in less than an hour.
If I were you, I'd consider popping for the $29.95 for this:
http://www.sailrite.com/Make-Your-Own-Winter-Boat-Cover-DVD I've used Sailrite DVD's myself in the past and find that they are very thorough and an excellent source of reference. I'm just getting started in a part-time canvas business and can use these tools very effectively.
Good luck.
Greg Murphy
capnm@mascom.com
S/V Amalia
1965 Cal 30