What are the guidelines and regulations for building a helipad for multiple aircraft? Are there any guidelines and regulations governing the ownership and construction of a multiple aircraft type helipad in 

a) the USA
b) Europe?
The FAA publishes an Advisory Circular on heliport design.  It applies to heliports serving helicopters with a single rotor.  I don't believe that there are any regulations regarding "ownership".  They just have to be operated in compliance with appropriate FAA, state and local regulations (but these can get complicated)