Pamela i'am not the person that made the green house but it looks like 6 window pans..4 to make the square (Bottom) and 2 to make the (top) with wegdes (triangles)to hold open the top window and 2 long two by fours on the bottom to keep it open and stable. one of the glass doors might even open if hinges were put on at the sides..for easy access...then you could put plant on the bottom too...Nice ideal!
Now I have just ONE MORE THING to look for when it's "Big Trash" day in town.....replaced windows! Hmmm....perhaps I need to call a window replacement company and get a word up on their next gig!