I hillbillied an indoor green house this spring. Found a bread rack like what they use in fast food joints to hold bread and buns, it had 11 of the big, heavy plastic bread trays with it. Everything was by the dumpster of a restaurant that had closed for business, so I appropriated it. Anyhow, I took the heavy, clear vinyl and cut lengths of it to hang from the top of the rack to the floor and then cut a piece to fit over the top. I taped the sheets of vinyl together at the sides, but there was still good airflow to keep it from overheating. We can fit 2 big trays of seedlings per bread tray and left enough room between each bread tray for the plants to have space to grow in. Set the whole business in front of a window in the kitchen and we started close to 500 seedlings and have now got nearly all of it in the ground going strong.
I love scavenging. Free is wonderful!