Jack rafters fill in the gaps between the hip rafters. One difficult part of this is getting them all level. I tied paracord from one hip rafter to the next as a rough level.

Another difficulty is getting the angles correct. These timbers join the hip rafters so they are angled in two dimensions. I used an angle measurer to match the angles on the hip rafters. Every one had to be individually cut to size as nothing is standard. I cut them all using a handsaw. A cut like this that goes in two different angles is hard to cut by hand, but after a while you get the hang of it. The key is to draw the lines on the timber, then hold the timber so that both lines appear straight, and cut down that straight line.

The other tricky part was holding them in place while I attached them. I used two pieces of 2×4 recovred from pallets, to grip either side of the rafter on the roof plate, while I held the top of the rafter against the hip, and screwed it in. It often took several attempts.

Step by step: