Here's a look at the rafter building process.  A template is drawn and formed on 2 sheets of plywood.  The first rafter 2x4s are cut and used as guides to cut 7 more just like it ... 8 rafters total.  Next the boards are assembled ... pounding in the rafter metal supports is a very tedious process ... about 15 hammer hits each, 22 supports to a rafter (front and back).  If you do the math that's 330 hammer hits times 8 rafters = 2640 hammer hits.  My arm was sore for a week.  Lessons learned would say that this process is not one for the books!.