If you are using a chain saw there isn't really any preferred order to cutting. We generally mark all the lines on the squared off end: side cuts, plumb cuts, chamfers for the housing. The backing planes may be cut before or after the plumb/side cuts on the end of the rafter.

If the plumb/sides cuts have been made you can make the cut along the plumb plane created at the Valley peak by marking the miter line (R5 in Hawkindale angles) and setting the saw blade bevel to the common rafter pitch angle.