I made a bag that was just the right size for my mat, most rulers, etc. Just did a simple 5" squares for the outside, added some pockets to fit certain rulers on the inside. I made it horizontal, with two padded handles so it would go over my shoulder. It was great....until I carried it a time or two! I then re-thought my idea, and made another one but vertical with the opening at the top. It is just a rectangle with inside pockets, but now my long ruler sticks out less, and pull less on the sides of the bag. I think I will add a snap strap inside to keep that long ruler in place. I gave the first one to a fellow quilter and she was delighted, but I am much happier with the 2nd one. It doesn't open and lay flat like you described, but it fits an ironing pad, cutting mat, large rulers, pockets for smaller rulers and rotary cutters and that really long ruler just fine.