For years, we have had a semi-circular patch of plaster just below the cornicing that cracks and loosens. It's been repaired repeatedly but returns each time and has done so again. I have been told by one of our best tradespeople that the problem is the "ladder" that holds the fascia board outside flexing. However, it is directly below a flat roof that has an asphalt and tile surface, and a railing around it, so there are several layers to uncover. How much work and cost would you expect to pay for a lasting fix?