Main Plaza Market, Karachi...there's a big shop when u cross the signal and go towards Radio Pakistan..on left hand. Name is Yaseen Carpets, if I remember correctly.
They deal in carpetting, trunk lining, floor lining, roof lining...and have a very large variety of material.
Ask them to keep the original roof of your car (if it is in good condition) and apply insulation material above it. Its a thick foamy sheet.