Cold frame over raised bed? Earlier harvest in TN?

[mari.beth]

I had a late start on my tomato plants this year because my hubby built two 4x8 raised beds for me which were not complete until mid-May. Therefore, I have a lot of green tomatoes and I am jealously looking at pictures of other people's harvests in other areas of the site. My husband said he thinks he can build cold frames using 80/20 metal and some type of plastic / glass that will fit over my raised beds that I could use next year to extend my growing season and (hopefully) yield ripe tomatoes earlier. I have been reading some on here and other sites about building and using cold frames, but have not seen any that fit over raised beds to be removed after danger of frost. (Maybe cold frame is not the right term for what I want to achieve.) I know that we would need to have some type of door / window on the sides for air flow / temperature regulation and a thermometer so we can assess the need to open / close / cover with a blanket, etc. Any suggestions (type of material, design, etc.) would be appreciated. I also would love any advice on how early I could put the plants in their permanent spots in the raised beds in zone 7a (Knoxville, TN) if I used cold frames.


(I am attaching a picture of the raised beds when I first put in the plants for size /shape reference.)