Brenden, the first thing to do with it is to test whether it will stand up to a summer's worth of sun. Some plastics do, and some will just disintegrate in a couple of months. So, leave one out in the sun for the next couple of months and see what happens. We solarize our soil at the school garden each summer, and the first summer, I bought a cheap roll of 4mm. plastic at Home Depot. That plastic made such a terrible mess, as by August it was blowing all around the garden in 1in. pieces.
Then I bought greenhouse grade 6mm. plastic which cost over twice as much, but held up perfectly for 2 years now, and we just put it on the beds for the third time.
Second thing is to find out if it lets enough light through, as it's sort of translucent and not clear. You could cut one and tent it over a plant for the summer, (don't enclose the plant though, it will cook) to see if the plant can grow with what light gets through. If you can put it next to an uncovered plant of the same type, you'll have a good reference. Don't forget that you'd be using your greenhouse in the winter, and the sun is much less intense then so you need all the light you can get to grow stuff in a greenhouse through the dark winter days.
