I've always liked the perforated headliner fabric that was common in the 60's and 70's. I'm thinking about using an off-white, which I think would compliment the bronze color of the interior paint. Using the ABS plastic as the backer would work, especially if it turns out to be a little thinner than the cardboard. I have a cardboard headliner waiting for installation, but it is a dark gray and I'm not that happy with how it looks...may be time for an experiment? The fabrics are plentiful on ebay and inexpensive ones can be found. Using spray on contact cement might be a good way to adhere the fabric to the ABS or cardboard before installing?