I've been reading Le Grand Livre de la Maison Miniature by typing sections into Google Translate, since my French is limited. The construction section, to my surprise, called for making the rooftop from Bristol board (I do wonder if I mistyped it...).
I've handled Bristol board countless times. It has many uses applicable to miniatures, but I wanted the rooftop to be made of something sturdy enough to take a certain amount of handling, several more moves in my lifetime (probably), and being in the same house as a large cat who is almost as clumsy as I am and doesn't let it stop him from climbing tall pieces of furniture. So, my rooftop is made of 1/4" plywood, left over from cutting the interior walls. The raised ribs are made from craft-store 1/8" x 1/8" sticks.
I couldn't find zinc paper anywhere, but I always have paint on hand. Using pictures of real buildings in Paris as a guide, I gave the bare wood a base coat of silver metallic paint, then added layer after layer of dirty washes in varying shades of gray. I have no experience with faux finishes, and was a little intimidated because I have never been a good painter (despite my best efforts to the contrary), but I'm very happy with how the roof turned out.
Obviously, 1/4" plywood is much thicker than Bristol board. The "seam" between the rooftop and the mansard roof will be covered by rain gutters painted and aged to match the roof.