They could start with a folded roof framing kernel.
Develop the roof framing kernel into a prism.
Develop the prism into a Trirectangular Tetrahedron.
Wire frame of Trirectangular Tetrahedron.
Develop the Trirectangular Tetrahedron into an roof surface with the pitch of plank for the tangent handrailing.
Then remove the one edge triangle of the Trirectangular Tetrahedron and label the direction of the ordinates for the direction of the minor and major axis of the ellipse on the roof surface.
Draw the minor axis of the ellipse on the roof surface.
Dimension the semi major axis on the roof surface.
Semi Major axis of ellipse on roof Surface = Radius of Tangents ÷ cos(Pitch of Plank).
Then draw the ellipse on the roof surface.
Drawing showing the relationships of the roof framing kernel, prism plane, trirectangular tetrahedron and the pitch of plank for the tangent handrailing.