A cold frame is a tried-and-true historical gardening device which allows a gardener to extend the vegetable growing season by providing what is termed a "microclimate." This microclimate is created by the cold frame's greenhouse effect; it captures the sun, heats the plants inside and insulates it from wind. Here's how I built a cold frame:
First, I built the basic box frame. The dimensions were dictated by the size of the glass window I had purchased, in this case an 18 1/16" x 32 3/16" basement storm window. But, I had to take into account that the glass will be at angle, preferably in the 30-45 degree range. Due to my window size, I had mine at about 23 degrees, because at 30 or 45 degrees, the frame would be prohibitively narrow. The final dimensions were 16 9/16" x 32 3/16". I used 1 1/4" wood screws at the corner joints, which made a much sturdier frame than the nails I used in my first attempt.
Next, I cut some lengths of 2x2's to screw to the corners of the box in order to provide some extra strength and bracing. Note that I also had to give the tops of the 2x2's the same slant to match the sides.
Now I can give it to the gardener in my family, so she can start with some early planting! :)