My brother is in the process of building his new house.
He comes with 2 questions about his master bath walk in shower.

  1. He is going to be installing multiple shower heads one of which is a ceiling fixture.
    He wants to line the entire shower with cement board for water protection but his builder is arguing with him that you only need to do the bottom half as that is where the water damage is most likely to occur.
    I said that being as there are multiple shower heads to stick to his wishes and use the cement board.

  2. He wants to place 2 mil plastic behind the cement board as a additional layer of potential protection. This plastic would be fixed directly to the wood studs and then the cement board layed on top.
    On the opposing side of the back shower wall will be the light switches located in the master bedroom.
    Is there any know issue with having the 2 mil plastic next to electrical wires inside of a wall.

If your having a builder do it and the builder does it your way, you may lose when there is an issue because you told the builder how to do it.

Anyway I would use yellow board on the walls.

The builder wants to use drywall on the upper half of the shower and the cement board on the lower half. This guy has not proved to be too bright so far.

Who is paying the bill? The customer should get what they want if they are willing to pay the additional cost.

As far as the wires and plastic you do not have an issue Code-wise.