I don't have a pattern for this but I've done this for a square pillow. The travel size pillow is listed as 14X10X3 at Target's website. But I would measure the one I'm making a pillow case for. So you want it to be big enough to cover 17X13. If you want the overlap to be in the long direction, cut your fabric 45X27. Fold back the end of the 27" length 1/4" and press. Fold it back again and top stitch. Repeat on other end. Place fabric wrong side down. Fold the 45" up on one end and fold the other end over that until you have the opening where you want it. Sew together with a zig-zag stitch the entire length. Repeat on other side.