On Aug 15, 3:15*pm, "gogmagog" wrote:
My mum n dad have a garage attached to their house.

Same here.

IMHE (did it to my small workshop, probably doing it to dad's garage
next) I'd go with a green roof. This is a clean scrape-off for the
old roof, down to the wall tops. Then span it with close-spaced 2x4s,
OSB on top of that, then 1" polystyrene insulation, geotextile,
waterproof membrane, 1" perlite or vermiculite, geotextile, then 3" of
soil. Plant with £20 of mixed sedums. Split & replant the sedums as
the grow, and within two years you can have it covered.

There's a group (Leeds Uni?) who have a downloadable PDF for about a
tenner that's the best guide to building a roof at this scale.