Frame door openings so doors can be added at some later date. Install railing and ladder. Add poly on bottom of top chords trusses to prevent insulation from blocking attic ventilation. Install soffit vents. Natural, rounded, bottom edge of trusses can be left exposed.
Tape joints with self adhesive mesh tape and fill with premixed joint compound.
Screw 2' wide slip forms along bottom of interior walls. Mix straw and clay and stuff into forms in 2' lifts. Leave studs exposed. Touch up walls after drying. Blow in cellulose insulation to a minimum of R-38.