I built a nice raised bed, 2 feet wide 10 feet long and was wondering if I could put plastic on it and grow vegetables in the winter. I live in Arkansas so we only have a dozen days or so where it gets really cold. I have good sunlight. Any idea what plastic to use? It has a frame all the way around that I had to build to put netting on to keep the squirrels out only after they decimated all my plants, so I can attach plastic sheeting or hard plastic but not sure which route to take. Any suggestions as to what direction to take, what material to use?

It's common to use a cold frame in a raised bed. It doesn't turn it into a greenhouse, but it extends seasons, so it could keep winter growth alive and lets you start earlier in the spring.

Search Google https://www.google.com/search?... and look at images. More examples than I cold describe. What almost all have in common is hinged tops, removable in warm climates.

You could probably make a cross-braces light frame and cover it with clear vinyl. Or buy some double wall greenhouse panels and lay them across the border.