I am adding a patio cover. I need to cut a 2X6 facia in a compound mitre at each end that are not equal. One end is the pitch of the roof and the angle of the deck edge that is not square. The other end is the deck angle and the perpendicular to the roof. That is: It comes off the roof in a pitch 90deg to the wall until the first support post. From there it angles about 30deg to the next support post while continuing the pitch. At the second support post the pitch flattens to the height of the end of the cover and runs parrallel to the wall. How do I measure and set up my chop saw for these cuts?