When finishing a basement should the ceiling or floor be completed first?
When adding new walls for things like bathrooms I will usually put the walls up first on the deck or slab this way if later you have a water leak and the underlayment has started to swell it is not trapped by the walls it makes repairs easier it is a real pain when the deck and underlayment is put down first and then there is a leak that damages the underlayment that is under the wall.