The frame was drawn in Sketchup then fully cut and jointed in the workshop before assembly. I decided to build the three lateral bents first and there was the advantage that the North end joins on to the existing barn - so this one went up first and was connected to the footing brackets as well as having several through-bolts into the masonry barn wall.
It was then easy to erect the middle bent using two of the purlins to set the horizontal distances and provide propping while connecting to the footing brackets.