Advice re roof build up

[Tom]

Hi everyone - we've only just poured our foundations, but as ever I'm looking ahead to see what else I can start worrying about. I'm scratching my head over the roof build-up as spec'd by the architect. There is a large service void in the "living wing" due to the presence of some 356mm deep steels forming a portal frame. We don't have this in the rest if the build, as per the lower of the two diagrams - I guess MVHR ducts would be run down inbetween the timber joists here?  Does the make up make sense? I guess it's a cold roof looking at the position if the vapour barrier? I guess what I'm asking is does this look reasonable or are there simpler/more efficient ways to skin this particular cat? E.g. use taped pir on the underside instead of vapour membrane/counterbattens/50mm rockwool?

Thanks in advance all