Research. Metal building condensation help

Hi, A friend of ours has had this suggestion. How's this sound? "I'm amazed how much input you've generated - you hit the jackpot with that forum! Re-capping what I thought: Crinkly tin, over vapour barrier or breather membrane (I cant decide which), over rigid insulation, over battened plasterboard (using battens to restrain insulation and then to fix plasterboard under.) This also creates a void for locating lighting services, unless you want to conduit to make life easier. Fix from above from upstand part of steel deck with synthetic washers and self tapping roofing screws. Consider using nylon or similar sleeves to the connections so you can tighten without squeezing the whole sandwich hard to the roof deck, which will help isolate the internal ceiling from the external roof deck. Before you do any work to the ceiling, strip out, fix windows, damp proof and generally get watertight. Then dehumidify and see what you get out. This should help mitigate moisture in the first instance. Once the ceiling is complete, further airborne moisture should be controlled with extract fan, air movement etc and dew point should be the wrong side of the vapour barrier. The only query I would have is whether to use a breather membrane or vapour barrier (which would be critical!) and my memory of college lectures on the subject is a bid shady... Will try to look into this for you, but time is a bit mad a the moment!"