1- Find the local “frost level”
and place piping below it
2- What kind of heat are you going to use?
3- Think about NON polluting anti freeze to protect traps like basin and toilets and other fixtures UNLESS the local codes allow for the traps to be installed below the frost line.
4- Is there a possibility of using electrical heating wires on domestic piping and drainage AND plenty of insulation.
When I install piping to exposed roof tank installations I use hair felt insulation to protect my fire lines (stand pipe and sprinklers) and my domestic lines.
On commerical applications where the building is closed on the week ends I use a heating coil inside the tank to prevent freeze ups.
Think about it like commerical work with a deeper frost level protection.
Allow for piping to pitch for complete drain down when needed on water service lines.
Increase the vent terminal to 4″ to make sure you dont have a hoarfrost condition