Here you can see on the left part of the roof where the sheathing was replaced after the fire..

We installed 2 x 4 purlins on about 24 inch centers from the eaves of the roof to the peak. There is 1 1/2 inch cut back at the peak for the ridge vent. The final purlin runs right along this so we have somewhere to attach the top of the roofing panels and also the ridge cap.

Murphy is of course working over time and several, I think 4 purlins on each side, fell right on top of the gap in the old roof boards, so we had to cut and install 3/4 plywood blocks in the gaps to keep the purlins straight. We used plywood, because if we tried to drive those 60D spikes through solid lumber it would just split.