Shirl, I think you need to ask this question on the web site 'Grow Your Own' (GYO) rather than GOY. This site is purely a gardeners blog whilst GYO is the magazine site with an inferior forum.

On the general principle, is polycarbonate better than glass, there are several things to consider.
Glass effectively lasts for ever (unless the neighbour's little boy likes playing football). Polycarbonate gradually discolors and becomes opaque.
Glass is marginally cheaper if you buy 'greenhouse glass'.
Polycarbonate is supplied in sheets with open ends. If you don't seal these properly with tape and/or aluminium strips, insects find their way in and lay eggs and gradually add to the loss of light and aesthetic appearance.
Polycarbonate is a much warmer material and better insulator, so your greenhouse can be kept warmer at night during the winter.
You pays your money and takes your choice, but I'd always go for the glass one in preference, just for appearance and the fact you can clean the glass every spring to let all the light through.

Shirl,
You have mistaken GOY for GYO I agree, but disagree about another forum being inferior - it depends what kind of forum and content you enjoy. GOY has many very experienced and generous gardeners who share advice etc because they love gardening so much. However, other forums may have a wider appeal and not be so narrow - ie plenty more that gardening can be discussed.