The frame on mine to attache the headlining was actually thin plywood, but the bottom half was gone.
I bought a new one from CTA ( Product Number 6920027 @ 33.82 EURO) http://www.ctaservice.nl/product/22316/ACHTERRUITLIJST-HOUT
but if you have a jigsaw and some 2/3mm ply you could make your own
Anonymous