DD_BobK wrote:
....

also....Metal roofing is not all that lightweight 20 gage steel would
be ~equal to 7/16 OSB.

You'd be hard pressed to find 20 ga exterior siding; 26 is far more
common inexpensive. Didn't look up actual mil thickness difference but
it's certainly quite a lot lighter.

That said, the question of what the lower chords are designed to carry
still remains and will until OP finds out unless he does just want to
wing it and see what happens...(not highly recommended, btw ).

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