for the headliner, I will assume it is foam backed cloth, seperating from the 'molded' carboard like factory stuff, (none of my A2 diesels have this type, they are 'vinyl' on molded composite) I recently re-did a 92 GTI that was cloth. So in that case. pull the whole thing out, strip off the cloth, wire brush degraded foam residue from cardboard(with fine brush / by hand). Clean surface very well, and wipe with damp cloth. Buy some 'headliner' material (preferably with 1/8" foam backing rather than 1/4" foam) Local "big" fabric stores have it, or I go to a 'automotive trim accessory wholesaler' it will cost ~$15 either place. Get some good 3M upholstery spray adhesive (~$7) and coat as per instruction. With two people, start in center and drop fabric onto molded piece, work out the bubbles as you stretch to the perimeter. reinstall. Takes only a couple hours. (w/o sunroof) For the Rabbit versions, I just remake a new vinyl headliner as per pre '81, with suspended metal bow's. The later rabbits have the pockets for headliner clips, and I get the clips from 'u-pull-it' pre '81 Rabbits, Same on Caddy, just need more work at rear corner. These vinyl ones take a little longer (4hrs), but are still ~$15 - $20 in materials Sunroof add ~4 hrs
The vinyl headliners are really nice, and will survive our 'anti-VW-winters' in PNW (100" of rain, largely running through fuse panel) (currently wearing 'irrigation boots' while driving)
If you have the 'vinyl' headliner on composite board, I would tear it off, (or at least any loose portions) and reinstall foam backed fabric. or find a solid one in a junk yard, The fabric looks great, and covers 'multitude of sins' (smudges, tears, holes).