Next, I traced out the curved pattern of the silo walkway's roof onto plastic sheeting, then transferred this pattern to the shingle sheets. I added a couple of inches along each edge, then cut the panels and bent the edges up so that they could be tucked under the shingles of the barn roof.
The end result is shown in the closeup of the silo walkway below. You can see the piece of Flexwrap at the ridge (over the flashing but under the metal shingles). With my dad's help, the remaining shingles were installed on the barn roof, overlapping the bent-up edges of the silo walkway pieces. The end result looks very clean and will be very waterproof.