This is a great idea–a greenhouse built from old windows from houses being demolished in the neighborhood. From the site:
I collected the windows over the course of a year and a half and the build took about 3 months, spending one day a week on it. I spent about $300 for the lumber for the frame and screws, caulk, latches, etc. That’s almost 10% of what a greenhouse kit would cost. The size I built was 7ft high x 10ft deep x 6ft wide. But the size of your greenhouse will depend on your windows and the time you want to put into project.
Talk about a great way to recycle! (Via)