Is this a hot rod, or are you restoring the car to original? First of all, do not adhere anything to the metal roof. The original headliner would have been attached to wooden strips that were part of the roof system. Since you don't have that any more, you need to put in replacements for those wood strips if you intend to put in an original type headliner. If you're doing a "hard" headliner, you will still need wooden bows to support a luan plywood base for the new headliner. In any case, the new wood bows should be cut from 3/4" hardwood plywood so they don't warp. It doesn't matter if your cuts aren't perfect because the headliner will hang from listings sewed to the headliner. The headliner will be about an inch below the wooden bows. Attach the bows to the metal above the doors with some of the new epoxies like some of the products from Evercoat. Is there any of the original wood left in the car?
No one lives forever, the trick is creating something that will.