I plan on building a pergola onto my front porch. Problem is, attaching to the rafter tails will make it too low(short). I want to attach further up, on the roof. Anyone know of a slick way to do this? It's a new roof so I'd want to disturb it as little as possible. I've seen 'rafter saddles' in magazines but don't know if this is the way to go or where to get them.