I just read "the new organic grower's four-season harvest" by Eliot Coleman. It was good and he had a good tip for building coldframes. Build 2 at a time. When you nail a triangle to a straight board you don't get a lid that is level with itself. I"ll draw a pic to clarify.
The basic build is to make a box, then cut at a diagonal on the ends. This turns it into 2 coldframes. The cut side goes down. You have a perfect top on each one for applying the glazing or a lid.
The only downfall is the side walls do not go straight up.