I bought the leatherette local from a company called Simon Boyd, you can get it online easy enough off eBay, but I needed to colour match it perfectly so bought local, £8 per meter and it's about 1.25m wide off memory, it's wider than the roof anyway, the old just pulled off with ease in one go and took all of 30 seconds. Mine had only just started to sag slightly in 1 spot. I then cleaned it up with a wire brush to get all that foam crap off left behind, just wire brush it till its smooth and down to the fibreglass (was messy but took about 15mins) then I aerosol spray adhesive (heavy duty stuff off eBay) used 1 can at £4 to do just this, sprayed all over the roof lining and material, waited a couple of minutes and lay it on and rubbed it flat, I had to lift it and redo it in a couple of areas (mainly edges and corners) to get rid off any wrinkles. My advice is don't let it stay stuck for long if you need to lift it as it goes off quite quickly.
Then at the edges I cut it into sections, pulled it over the edges and glued over each piece onto the back. Where you see the indents for sun visors etc it was easy. The hardest part was the 4 corners.
You can't use staples it's too thin!
Hope that makes sense