Speculation - The glass roof... is the solid roof! Just throw a "solar sunshade" under it. Remember how Model X owners were given deploy-able sunshades? https://www.tesla.com/sites/default/files/pdfs/modelx_sunshade_installation.pdf Tesla could combine a sunshade with the same thin solar cell film used under Tesla glass roofs to make a solar sunshade. Piece 1 could be deployed inside the car over the panoramic roof, and be used even while driving, constantly generating solar energy. Pieces 2 and 3 cover the front windscreen and rear windscreen, and are only"deployed" when parked. So essentially there's no need for a metal roof. Just throw up the solar sunshade when want to stop looking like extra crispy Colonel Sanders. The middle solar sunshade could be included, while front and rear sunshades are sold separately. They could also be given out for free to day 1 reservation holders, as the free solar umbrella gimmick Elon spoke of deploying while parked.