Moisture Barrier/Plastic in Ceiling

[Matteshus]

I have hired craftsmen for an extension of a house. Now to the question, we have come to a bit of a disagreement regarding the moisture barrier in the ceiling. I believe it should be above the lattice panel to create an air gap against the ceiling, but the craftsman has placed the plastic under the lattice panel and claims that "that's how it should be," not even open for discussion. What does the expertise here think?

 

[useless]

It doesn't matter.

 

[McNulty]

If pipes for electricity are to be run in the ceiling, it becomes much more cumbersome if the plastic is under the sparse paneling.