Originally Posted by Gringo
the extra material goes around the front of the top to finish off the edge. Usually sewing around a piece of windlace cord. Can be stapled around a piece of rubber hose as in fuel line or vacuum hose.
While you can use windlace sponge rod to make the finished edge, the original top would have had extruded plastic header welt (also called header strip) sewn inside of the fabric. It is still available from ARO convertible tops:
If you saved the old stuff from the original top, you can have the new fabric sewn to it. I think it looks way better than anything round to finish off the top in front.
Here's what it looks like: