We took a hand-selected 2x12 - 16' long, and cut it down to 14'. Then we tacked a piece of PVC sprinkler pipe at either end and pulled it to the middle in order to form the bow. With that held in place, we marked the line with a pencil.
We also marked the center line, then cut the first half with a jig saw. Instead of taking the risk that the sway would not be consistent on both sides, we took that first half which was cut out and used it as the template for the second half. Re-marked the line and cut the rest of the arch.
The tough part is cutting the rafters. Each has to be individually cut for the angle and birds eye. But they work in pairs, so you can reduce the cuts a bit.
What I mean here is that assuming you have 4 mid-span rafters as we do, the two at either end should be identical. Then the next 2 (the middle ones) should also match. But we did find that we were off enough from one side to the other that once we had the west ridge of rafters done, we had to re-measure everything for the east side. Make sense?
