Check out these handy tarps that I have been using...
I usually buy it in white, but they were out so I bought brown instead. I usually get them at a big box hardware store at an economical price- under $3 each.
I like the fact that they are water, mold and tear resistant. Hmmmm... I hope they aren't releasing any funky chemicals into the room. The owner of my favorite garden supply shop would know if they do, he's good like that. I'll have to ask him next time I visit.
Another reason why I love them is that I can toss them into the washing machine if they get dirty and hang them to dry.
They serve other purposes too. When I transplant I use them to transplant on so I don't make a mess on my work table. They protect the floor from spills and I can even vacuum them with the plants in place. It's a tad tricky but possible. Sweeping them is easier. If it doesn't fit the grow area you can either fold it to size or cut it as I have done. I'm glad I stumbled across them. Next time I go there, I'm going to stock up on the white ones since they seem to be the most popular color...it could be that some other growers have discovered their handiness too.