I used an auger to clear a post hole, stuck a cardboard sleeve 36in deep and filled it with concrete. Set an anchor for a 4×4 in there.
Then I took a 4×4, cut it to length and drilled out a socket for the bottle jack stem to sit in. This is the brace to push up on the joists to lift the roof.
Then I put a 4×4 in the post anchor and aligned to the lifted post. Ran an auger drill bit through the good wood. Bind these together with threaded rod, washers and bolts.
Repeat for 3 posts, each a mildly different story that rhymes with the first.
I think it worked, or at least is a solid C grade. Some of the rafters in the roof that had shivered from being unsupported came back together, so some marked improvement is in place.
Still cant keep the goats out of here though. They are persistent.