This is a very cool idea from Starving off the land. If you make one of these you can get your seeds out earlier and have fresh salad greens or spinach from the back yard earlier. Cold frames also help to extend the growing season when you put greens in them. They help warm the soil from the sunlight and keep humidity levels higher so you can keep growing long after the garden is done for the season and this is a pretty easy cold frame to make.
Cold Frame diy
http://starvingofftheland.com/2010/03/well-constructed/
W4419 Hd Window Well Cover
Cold Frame Greenhouse
Juwel Cold Frame 1000