I've made several and have taught others. I do it two ways:
1)add borders and sew them to the quilt with the raggy part on the same side as the raggy blocks. Then I stitch 1/2" seam around the outside border for stability and clip to the stitched line
2) Cut the border twice as wide, then fold in half lengthwise. Sew the raggy seam on the raggy side of the quilt. The snooth end then becomes the final edge of the quilt. I run a stitch along the edge, but don't cut it.