If you can get some of the coated particle board shelving material (called Melamine here in Australia) used to make kitchen cupboards, cut a piece slightly larger than the largest paper you'll be printing on. It is generally about 20mm (3/4 inch approx) thick.
Cut some pieces of thin ply or masonite - make these about 50mm (2 inches) x 25mm (1 inch) x 6mm (1/4 inch). Glue two of these at right angles across the top left corner of the melamine base (cut as above), so that the 1 inch face joins the 3/4 inch edge (at the corner of melamine)...bear with me now - this is a lot easier to picture with the pieces in front of you! You should have an "L" shape across the corner sitting 1/4 inch higher than the base. This is where the top left corner of your photo paper will go to keep it in place
Put another single piece of the 2 inch x 1 inch ply about halfway along the top edge, another piece halfway along the left edge of the base. These will help keep the paper lined up with the top and left edges.
As the melamine base is generally shiny white, you can draw in the outlines in pencil, of common sizes of photo paper you use. This will help when setting the image size under the enlarger. I have made such an easel at 16 x 20 inches marked off (in inches) 8x10, 8x12, 11x14, 12x16, 12x18, 16x20 (8x12 and 12x18 are for printing some 35mm full frame wedding work that I do).
Finally get some thick black paper to fit the easel to place under the photo paper when exposing it to stop light being reflected back through the photo paper....Phew!!
Sorry that this was a bit long winded, but I haven't tried posting a picture on this forum yet (no digicam!).