Hello Trudy,
What kind of tools do you have? That helps us to make practical suggestions on what kind of paper safe to make. If you have access to the king of shop tools - a table saw - theres no limit to what you can make.
I find 1/8 inch tempered Masonite to be ideal for paper safes. Rip some 1-1/2 inch high sidewalls out of Masonite and glue them to a lid and base, keeping a 1/16 inch gap between the sidewalls. Do the bottom first. After the glue is set, use a few chips of matboard as spacers between the sidewalls when gluing the lid on.
There's no need to use nails, a good woodworking glue is just fine. You don't even need clamps (although they help), just use weights to hold everything together until the glue sets. Leave a 1/4 inch overhang on the lid to make taking it off easier. After it's done, spray paint the sidewalls flat black.
I just did a quick count... I have 21 paper and film safes ranging from 8x10 thru 20x24, and 12x32 (for landscape format prints). When I get some time, I'll add a page to my TechBlog on how to make 'em.
Maybe I ought to make some "Kits" for sale. Hmmm...
Reinhold
www.classicbwphoto.com