When remodeling a bathroom, we Highly recommend starting with the old pipes behind walls and under floors because that is the most important part of any bathroom and most customers never think to run a camera, most people only fix what they see, and out of sight ! out of mind !    Many houses flipped on a real estate market have this problem, everything looks great on top, yet there may be a surprise behind the walls and under the floors if there is cast iron pipes, or poorly installed PVC pipe which has bellies on the bottom or back pitched sloped drain pipes.

Copper or Pex pipe both have their benefits, New Pex A type is the best and is very flexible and affordable for in house use.  Copper for non freeze areas is ideal for outside because of its heat and durable resistance in the hot climates.  

Never, Never and Never use CPVC, major issues with this material, stay away from it, it becomes brittle and breaks.  Especially the CPVC valves!