I have a lot of 1by that is old (11.5 or 11.75 wide) but it is painted - some on one side, some on both sides.
These would be perfect to replace damaged roof sheathing.
My concern is that the paint is a vapor barrier that could result in excessive or reduced cupping if moisture enters the equation.
If painted one sided, I think I’d put the paint side up so the wood would be free to dry out on the exposed bottom. In fact, if there was a leak in the roof, the paint would work in my favor (I think.)