glass or plastic?

Glass is good and there are many 2nd hand houses going cheap or even free. If the kids throw stones though....
I spent 150 building a wood and twinwall polycarb on the back of the office at home only to find a similar sized glass one in the local rag for 30 pounds.

On cost, use plastic (polycarbonate) only if you can scrounge it or get it second hand (eg old bus shelters). I was lucky because my work (museum) is being refurbished, so loads of polycarbonate, clear plastic etc from old display cases. I'm right next to a public footpath through our allotments, so probably wouldn't consider glass myself. Don't drive, so problems getting new materials up if anything did get broken. Tried to make it all as indestructible as possible first time round.

My plots border the edge of the allotment site with public footpath along the entire length so I have used polycarbonate for the roof and side nearest the path and glass for the remainder.  Purchased the polycarb from Formerton Sheet Sales in Southampton (they deliver) - 6mm Lexan Clear Twinwall.  If you send them a Blue Peter diagram with all the dimensions for the panels they laser cut to size.  Fortunately no stones have been lobbed at my greenhouses yet...but I am friendly with the retired folk living the other side of the footpath who keep a very beady eye out for any/all goings on!