I think you are right that this section does not require the roof to be bonded.
What about 250.104(C)? I think it does not require a metal roof to be bonded if it is not "interconnected to form a metal building frame". I'd say that if the metal roof is attached to metal building framing, the framing should be bonded/grounded. But this whole discussion is over a non-issue in that case!:lol: But if the metal roof is attached to wood framing ... then I don't see a code section that requires it to be bonded.
FWIW, this thread was never about a code requirement; the OP was about best practice. So far I've not been forced by any AHJ to bond a metal roof because I was installing solar. So fingers crossed I don't have to remember these code citations anyway...
Kind of, the OP brought equipment
grounding conductors and ground rods into the question which makes it code related. They also asked what was acceptable as well as best practice, and determining acceptability is part of the code.
The code does not define the term "structural steel" but my take it that if it is not a structural component then it can't be structural steel. Cladding, windows, doors, and roofing materials are not structural since the structure will stand without them. Beams and other load bearing members are. Steel I-beam, that should be bonded in.
To take this out of a code context and just look at it as a best practice, it is possible for metal roof pans to be energized by a PV conductor falling from the array. That's not much of a stretch. That being the case we should want to ground the pans. Can we add the pans to the EGC system? Not easily, there are no products that are designed to do this without modifying the roof. The roofing manufacturers won't allow physical modifications. So we are kind of stuck.
However 2017 250.4(A)(4) still states "normally non-current-carrying electrically conductive materials that are likely to become energized shall be connected... in a manner that establishes an effective ground-fault current path."
NEC 250.4 lists very general requirements, the following sections provide the more specific prescriptive requirements to comply with 250.4. Read the text right under 250.4.
The following general requirements identify what grounding
and bonding of electrical systems are required to accomplish.
The prescriptive methods contained in Article 250 shall be
followed to comply with the performance requirements of this
section.
The later sections in 250 add more definition to the general requirements.