A plumber is typically on site from the very beginning of a project -
from BEFORE the footings go in (to do drain lines), through rough
framing (to install water lines), through roofing (to install vent
lines), through flooring (to install tubs), through tiling and glazing
(to install trim) until the very end of a project - commissioning hot
water heaters, radiant floor heating, gas stoves, ice makers on
refrigerators, etc.    As such, choosing a plumber, with whom you
are compatible is paramount to an enjoyable construction

Additionally, there is nothing more insidious to the destruction of a
building or the growing of mold as a tiny water leak, and nothing
more explosively dangerous as a gas leak.  Foul smells can
emanate from improper adherence to drain line or vent line or
trapping standards.    Inability to adhere to published criteria on
placement of clean-outs could lead to expensive repairs down the
road.  Not distinguishing between storm water, grey water and
waste water could lead to substantial fines (and a waste of water
and/or sewage treatment resources).    Fortunately, a skilled,
knowledgeable plumber will have comprehended all 316 of the
National Plumbing Code so that you don't have to.  

The plumber will also have to interface with any
whole house
filtration systems or solar heating systems or fire sprinkler systems
and with steam rooms, water features, spas and pools.

Besides choosing a professional plumber wisely, the choices that a
homeowner gets to make in the plumbing arena include
a) type of heating - forced air or radiant floor
b) type of water heater - conventional or a
tankless water heater
c) trim - tub spouts, rainhead shower heads, hot/cold water taps