Intro: Coldframe From PVC Pipe and Coroplast
I have made several of these small cold frames and had great success with them. We can grow cool weather plants all winter long in Oklahoma. I've had plants survive 9 degree nights before. You can add a layer of bubble wrap on top of the plants to protect them even more during really hard cold spells. I have never really run a cost on these, I just made them because I want my salad all year long and my wife likes to garden.
I built this out of 1.5 inch pvc pipe and 4mm natural coroplast. The 'Natural' Coroplast is slightly translucent. It's very easy to cut with a utility knife. You might have to go to a plastics supply house or a sign supply house to get the coroplast, not sure if it's a regular home improvement store item. I used self drilling, self tapping screws designed for attaching lath. They have a large head that looks like a built in washer. I didn't glue any of the pipe together, just tapped it together with a wooden mallet or by banging it on the driveway. Kind of tried to keep things squared up as I went along, but nothing is really critical. I always build the top first, then fit the body to it to make sure the body is not too big for the top to fit.
I have included a drawing and a cutting ticket.
You can see an assembly movie here: