I am installing cypress ship lap siding.  One side of the house has stairwell going from main level to the basement.  We are using interlocking pressure treated corner boards, I need to know the fastest and easiest way to lay out and cut ship lap.  There is a brick ledge that comes from the backside of the house to front, but it has a curved radius half way through it.  One idea is to cut a piece of tyvek to the radius, level it, and tack it to the wall.  I have already established a layout on the other side of the house.  I can transfer the layout to the corner boards of this side of the house and snap lines across the tyvek and use that as my pattern.  Is there a better way?