I am remodeling my old house bathroom and I am installing a new tub and shower base. My wife will be taping the cement board and drywall and wants me to install the board at the ceiling first and work down toward the new tub and shower base. She does not want to stand in the new tub and base and work. Is this a no-no? I had planned to start at the bottom and work up and cut the last piece to fit the ceiling. Opinions and comments appreciated.