The location isn't the greatest, but I'm not moving it today!
Anyway- what I did: I had salvaged window that was in the shed, it came with the house ( several actually).
I also had about 40 reclaimed bricks which also came with the house. I stacked the bricks up double and simply layed the window on top. Because of the location and the fact that it isn't sloped, the bottom half of the frame was shaded. I took several of the taller bricks to raise up my pot to the level of the sun light. There is a quarter inch gap around two of the four sides. I don't know if that will be a problem yet but I have sheet plastic to lay over the whole thing on colder nights. I removed the window screen and simply slide open the window to get to the plants!
In the coldframe right now: sweet peas, lemon cucumbers, swish Chard, and pie pumpkins.