A guy at our club had his wife sew up a banner. He attaches it to the plane with a servo-actuated hook. The banner is laid out on the ground so his take off run is parallel to the banner going from front to back. As he picks up take off speed and heads down the runway the banner “rolls” off the ground to trail the plane. By using a plane with a short take off run and long enough rope on the banner, the plane is well into the air by the time the banner has been fully lifted of the ground. When it’s time to land he does a low pass to drop the banner first. Hope that description makes sense?

As for actual banner construction, I don’t know how it was done.