I need a link to the section of the NYC Buildings Code for fence construction in front of a condo.?

You need to call the building department with the exact address.

All that r3 means is that 3 families can live on the lot.

I would guess you can build up to 4 feet high and that it has to be see thou. There will be laws for building materials too.

that can vary from on neighborhood to the next call the zoning commission office there and they can give you the correct one for the address

call you local building and safety office and ask them, they should be able to provide for you. they are probably the agency that will inspect and approve of the installation