Dimensions sound more like a large coldframe than a GH. Easy to construct out of some 2x2s or 2x4s, 4 corner braces, a couple of hinges and a couple sheets of double-wall polycarbonate available from any GH supply. Be sure to also include an auto vent opener for the lid or the plants get cooked.

http://www.greenhousemegastore.com/product/10468/greenhouse-polycarbonate-sheets?gclid=CjwKCAiAtorUBRBnEiwAfcp_Y8CXWQxWn7DTkJqTiG-ptlPgEJyOJJ3RenA5RtJ1FgJkiGwitr-P5RoCwKcQAvD_BwE

You might check out the Greenhouse forum here for 'cold frame pictures' as I recall many have posted over there.

Dave

Can you get hold of any old sash windows? They can make good frame lids.

The only side you should need to let light in would be the south side. This is how I did mine.

What is it covered with?

twin wall polycarbonate.

When weather gets better I will post a pic of the cold frames I built. VERY cheap and easy. I bought a huge roll of opaque white plastic from home depot. I then built a square base out of 1-1/2" PC. I added a center piece to the height I wanted and then drilled holes in the base on 2 side and put pieces of pex in curved over the top and down the other side. It has curved sides. I build a 4' x 5' x 3' frame for about $20 or less. Lasts years and works great!

pics