Okay, I just blocked this shape into three sections and have a feeling for where I want to go with it.  The sheet is placed over the raising stake and I will begin to delineate the distinct forms that will be shaped by hammering an offset around the drawn line on the opposite side of this sheet. This stake is a piece that I simply flame cut out of 1/2" plate steel then ground down a tapered rounded edge around the top radius.  This shape allows me to follow a line drawn on the reverse side of the sheet, while hammering.  The fan shaped edge of this stake allows me to stretch the metal along a straight or curved line.  I can simply roll the sheet on either side of the peak of the stake as I move along the drawn path.  If this stake was configured straight across then I would be hammering from the reverse side (convex portion over the blade).