Peter Parry wrote:

When we built our garage I lined the roof with plasterboard sheets
and painted them white for the same reasons you want to. The
plasterboard was simply screwed in place - no skimming or filling.
It was simple to do (although you need some props and assistance) and
looks as new after 12 years. No cars are in the garage though :-).

Hmmm, plasterboard is fairly heavy stuff and my poor old neck and back
aren't too good these days, but I haven't yet checked to see if it's cheaper
than thin ply.

Thanks

Rick