I've been using a tatty cardboard box for a laptop screen for use while solar imaging and wanted to do a better job. There have been a few threads of people using plastic Correx board to make one which is what I've just done. I bought a 8' x 4' sheet from http://www.the-aluminium-shop.co.uk/correx-sheet The sheet is usually supplied rolled so it will be necessary to un-pack and leave to flatten over night or in the sun to warm up for approx 1 hour. The attached .pdf drawing shows the design and