If space is a big issue purchase a blind for your window or wall---the plastic kind that roll up. Unrole several feet of it and glue flannel to the room side of it. When you don't need it, you can just give it a tug and it will roll right up out of the way. If you can attach it to the all or ceiling you might want to get the widest one possible. Thin double stick carpet tape works well but you might want to get someone to help hold the flannel while attaching it or roll it around a large dowel, place the bottom on the bottom of the blind and just unroll it onto the taped blind.
You can also make one that will fold up out of the way with one of those folding cardboard cutting mats (available in most fabric stores--they're used for cutting out clothing), a peice of flannel the same size, two curtain rods that will open to the length of the cardboard, and several binder clips. Use the binder clips to clip the cardboard, rods and flannel together. The rods will keep the cardboard from folding up until you're ready to take it down.