Glass allows more light through than polycarbonate so the glass house will generally absorbe more heat energy. However, if you remember what long spells of bright sunny weather were, they can get too hot and plants can scorch!!!! Shading is possible in these situations. Both our greenhouses are glass because it is cheaper than polycarbonate but I would prefer the latter. If you have children or potential grandchildren running around the polycarbonate is safer.

I bought a cheap polycarbonate cold frame this spring and the twin wall polycarbonate panels are already disintegrating. They will hardly hold in the frames as the edges are disappearing. I wouldn't recommend it at all.

Probaly not the polycarbonate, Beattie, but the glue that fixes the aluminium frames to it? I have that with a not so cheap cold frame from Lidle. Had to re-glue them!

Polycarbonate also blocks ultraviolet light, making life tough on those plants that require it for their metabolism, and making hardening off harder for those that don't.

My cold frame came from Lidl, Bulba, but no glue was involved. The polycarb sheets slide into grooves in the aly frames (and the aly frames screwed together, but the screws tend to pull out, so I've tied it together with string.....), but the polycarb is disappearing from the edges, eroding away ....
I doubt that it will see the winter out.

thanks to you all for that...I think I will go with glass..is it easy to get shading and is it expensive?

The cheapest sort of shading to buy is like a whitewash that you paint on the glass - at the end of the season you need to clean it off, though. You can also buy netting to fix to the inside or outside of the greenhouse. At the top end of the scale you can buy 'roller blinds' of shade netting or slatted wood to fit on the roof ridge. Probably the cheapest is old net curtains hung on wires fixed to the inside - you can be as inventive as you wish.

very interesting....thankyou :)