The stringers, running lengthwise and sitting on the curved end walls of the shell, are supported by two intermediate trusses. Stringers and trusses are both made from boric acid treated 2x4 lumber. The overhanging ends of the stringers are tapered upwards to improve their appearance.
Standard galvanized metal framing brackets were used for connecting trusses and stringers to ferrocement and to each other. Quarter-inch galvanized carriage bolts were used for attaching the metal brackets to the ferrocement. 'Grabber' type wood screws were used to connect brackets to wood.
Here a truss sits in a notch cut in the ferrocement wall - the wall bears the load directly. The modified metal framing bracket stabilizes the truss in the notch, but is not load-bearing. Quarter-inch galvanized carriage bolts were also used for bolting the trusses together and joining the stringer halves.
The trusses were "built to fit" to support the stringers in running straight and true from end wall to end wall. The lower crosspieces of the trusses are dead level. The angles and lengths of the upper truss members were determined by what was necessary to support the stringers properly.
To shape the curve of the roof and support the roofing metal properly, flexible battens were screwed in place across the stringers. The battens are clear straight-grain 1x3's which I treated with boric acid wood preservative (they were not available pre-treated) before putting them in place.
All battens except the front-most one were laid perpendicular to the stringers. The front wall is not perpendicular to the side walls, so the front-most batten meets the one behind it at an angle at the East corner of the roof structure.
All together now...trusses, stringers and battens in place, looking towards the front door opening. The right front truss end, rather than resting in a notch in the wall like the other three truss ends, sits on and is attached to a notched vertical support that is bolted to the wall.