What are the FAA regs regarding landing a helicopter off airport?
There are no Federal Laws prohibiting landing rotor craft off field.
14 CFR 91.119

(1) A helicopter may be operated at less than the minimums prescribed in paragraph (b) or (c) of this section, provided each person operating the helicopter complies with any routes or altitudes specifically prescribed for helicopters by the FAA;

Part B and C, for reference

Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:
(b) Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft.
(c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.

However, state laws, local laws, zoning laws, etc. change from location to location. You need to make sure you plan where you are landing beforehand and check these laws.
For example, in the State of New Jersey, helicopters can only be landed at the following locations:

Permanent public use heliport or vertiport
Permanent special use or restricted use helistop or vertiport
Temporary helistop or vertiport

(Reference)