These are easy and very satisfying to make; it's just straight accurate sewing and you can use up any gorgeous fabric or material you have lying around. I made 2 different versions.
This one was my first attempt and I used some neutral but embossed fabric and backed it with fake leather. I made it up as I went along, but here is how I tackled it:
Cut 6 or 8 or 10 (depending on how many placemats you need, obviously) rectangles from both top fabric and fake leather (or other fabric) for the underside; measuring 45 cms x 35 cms (17½ ins x 13½ ins); incorporating a 1cm ( or ½ inch) seam all around.