Thought I would share a little project with you that we are using here at the office for our 4-H cooking club. It's a small inexpensive coldframe that we begin some kitchen garden type plants in for the class. Things like herbs, lettuce, onions, leeks and other food plants. The kids can pick and use fresh product in their dishes and become acquainted with the process of growing food.
This was constructed using two recycled storm doors. The doors are attached to a lumber frame custom made for the door sizes. This happens to be an 80" x 53" box made from 2" x 10" lumber. There are two identical boxes stacked on top of one another and the top can simply lift off in order to till the bed at the beginning of each season. The on door is automatically ventilated using a automatic opener as seen in the small picture. This project was completed for less than $100 dollars in materials.