Good luck, I hope to see pictures when you've finished
@ tonguello: I used potting soil
It was a bit too dark when I first put it down, but as the soil dried, it looked better. When the soil dries, it will crack a little, so you'll have to fill the cracks up a few days later.
@ Tiermann: The sunporch is actually supposed to be attached to the other side, so that will fit nicely.
The sandy textured plastic is not sanding paper in any case. It's not that rough at the touch at all. My best guess is that it's used as some sort of vinyl flooring. I think it will remain a mystery