External dimensions of the house 13200*8800, inside carrying transverse walls.
The walls at the moment is built as in the figure, except for 3 rows of block on the gables, portals over the windows and the partition – the truss will be supported by a temporary prop, which would not interfere with the partition "maneuvering".
Instead of ridge beam truss, (plywood overlays are not drawn at the nodes), the span is 6 meters... At the height of the truss 1560 strength should be enough to spare. And there is no point in reducing the height, it is logical to tie it to the puffs, you only need a cubic meter of material per truss.
The rafters 50*200 mm, pitch 620, tie beams 50*200, but may be enough and thinner?
Truss girders made of two boards 50*200 or better solid bar 100*200?
How to connect rafters with wall plate? On the one hand the system would be like a lean-to, but on the other hand possible small deflection of the truss and the appearance of pulling the load on the walls. That is, a sliding connection is desirable. Is it worth using the newfangled metal sliders?
The general idea is correct, but the dormer is done slightly differently – his ridge is supported by "cross bars" that hang from the twin adjacent rafters.
About the spread if you mount the mauerlat on studs – make a few millimeters more in diameter, depending on the calculated deflection of the truss, usually this is enough.