Neil - I'm so glad i'm not the only one
I bought a greenhouse which stood without glass for about 3 weeks until my dad came down and told me i was stupid ( charming !!! ) and promptly showed me what to do - which is one of those things that when you know it - it is easy - but until then it is unfathomable
Am sure you will crack on like a rocket ....
With the glass in place grap a w pin Pop the top ( end bit ) of one side of the w under the greenhouse frame and puch the bottom bit under/next to the glass - the middle bit of w then holds the glass in from the top and you just ping the other end of the w under the frame
- i really hope that helps !!! - i know exactly how fustrating it is