I came up with the pattern myself based on what I wanted.
It's easier to just tape paper together. Then draw a rectangle depending on the size you want the placemat. I used about 18x13. Then I took a dinner plate and rouned off one of the corners with a pencil. Folded the paper in quarters and cut the pencil mark...that cuts all 4 rounded corners equally at the same time.
As for the design of the table topper, It's just something I drafted. I started out with 3 10" squares and used PaintShop Pro (my graphics program) to fill in squares and triangles in all different ways. I Scanned all the material I wanted to use, and used those images to fill in different sections. The program sure made designing a lot easier.