I built a home made greenhouse over a 10x20 raised bed. One side is my house and the other three sides I built with wood frame I covered it with 6 mm plastic sheets. Because I am an amature I am surprised how nice it looks. Even my woman who thought that I lost my mind liked it. I have a question . Right now the sides are single sheet I could add another sheet to make the wall double sided with some air between the sheets. What are the pros and cons of single v. double.