For plumbing, any new piping (even replacing existing pipe with new) would require a permit.

Estimates are bout 400k for full gut remodel (hvac, plumbing, electrical, roof, mostly new windows, kitchens, and baths, minor re-framing) New plan is for (2) 2B1B units and will rent for 2k and 2500/mo. 1 unit is a larger 2 bedroom.

Plumbing, Electric, HVAC, Drywall, Gas etc.

Tenant shall properly use, operate and safeguard Premises, including if applicable, and landscaping, furniture, furnishings and appliances, and all mechanical, electrical, gas and plumbing fixtures, and smoke alarms, and keep them and the Premises clean, sanitary and well ventilated.F.

Then go price your labor plumbing electric, roof, finish outs, and landscaping.     

I handle all contractors on defined work progress, i.e. demo complete, plumbing rough-in complete.  

Still you’ll need to fix any plumbing, electrical, door etc type issues which likely are in bad shape.

Roof, plumbing, hvac, water heater, etcE.  

Soon after moving in we found that we had some plumbing issues.

You also become responsible for making sure your tenant has a livable space - keeping all the major systems up and going - so hot water heater, AC, the roof, electric, plumbing, etc.