If you go the black plastic route use the material available in garden stores or the garden dept of Home Depot. It is very durable and can be doubled . Get a closet pole, cut tow the sane length and staple the plastic sheet (or blackout cloth) to top and bottom. Attach "L" hooks of appropriate size above the door or window and set the pole on them when needed. When not in use just roll up like a scroll. Simple and very inexpensive.