8x10s (with the wide face plumb) would be less prone to buckling in a roof truss, since chord buckling is restrained in the plane of the truss. But buckling is not likely to be an issue since the compressive elements are either short (struts) or restrained in both directions (rafters aka upper chords).

Maybe it wouldn’t be such a bad idea to consult a structural engineer. Certainly I would recommend learning more about how trusses work. One good place to start is with the historic truss series in Timber Framing, soon to hit the stores in book form as Historic American Roof Trusses.