For a straight section, measure the maximum free height that the fence must occupy, and the height of the fence. Take into account if there is any obstacle that limits the height of the fence.
For an L-section above a wall, measure the maximum length of each side and the width of the wall. We already took care of the calculations so that the fence follows the center line of the wall.
For a section in "U", follow the concept of the section in L. Check that the width of the wall is the same in each section.
For a typical stair wall run, simply measure the length of the flat part of each step, and the jump height of each step