In this video, presented by Mark Powers of “This Old House,” educates crafty gardeners about each of the steps involved in making a “cold frame” extension to their greenhouses.
Begin by laying the window over your wood in order to measure its long edge and ensure a proper fit for the frame’s front and two back portions. The purpose of using a window is that it will serve as the lid of your cold frame, allowing your plants to absorb sunlight while remaining protected from the elements. The video then goes into detail about how to make the proper cuts and measurements to finish out your cold frame, noting that you will want to end up with an angled frame.
If you’re worried that this will be a permanent fixture of your garden when you have a more seasonal need for it, the video covers a tweak to the construction process that allows the frame to easily and safely collapse for the purpose of storage in your attic, shed, basement, etc.