The best bet for any type of cold frame or greenhouse, I think, is a minimum-maximum thermometer that helps you track to make sure it's not getting too hot or too cold. They are pretty cheap and they display the minimum and maximum temperatures reached, as well as the current temp. Here is an example among many models available:
Good advice from Steve. Be sure to place the thermometer sensor at the level of the leaves, not on the ground.
thank you all for helping me!
You're welcome. Good luck.
i have the thermometer bought i have to dig the foundation into the ground and install the bricks and i am ready to move the plants from the house to the cold frame, the cold frame is primed and painted two coats on the inside and now i am going to paint the outside to match the trim on my house dark green!