Cold Frame Using Old Window Building Part One

After pulling out my old window, replaced it with a much greener one, I wasn't sure what I was going to due with it. Kicked around the idea of a cold frame, I learned a friend on-line was in zone 4 and uses theirs through the winter for winter hardy crops. I explored the idea further and remember one of my old Mother Earth magazine had a article in it some years ago about cold framing.

I would really like some ideas on things to use inside to gather heat during the day and keep it warm during the night? Do you have/use a cold frame? I am in zone 5a, what crops would you use?