I think that I have found software that will help people to design new solar cookers.
It is called art of illusion, it is a java program, it is free and it is cross platform. I have found it fairly easy to use.
More info can be found at this link. and a downloadable scene file that you can use in art of illusion to do your own design work http://www.instructables.com/id/SHDDXHZFR0ZHCZX/
http://www.youtube.com/gaiatechnician has several new videos on using the art of illusion software in solar research.
They can be found in the most recent videos. I upload an art of illusion file here to get you started
Thank you
Brian White