Screw two pieces of 1x4 together with a slight overlap — one leg registers against the bottom edge of the cabinet, the overlap holds the door at exactly the right reveal while you fasten the hinges.
When drywall stands proud of the door jamb, casing rocks and gaps. Mark the casing's footprint, score inside that line with a knife, and break out the drywall behind it with a hammer — the casing lands flat on the jamb, and the crushed zone stays hidden.
Let the finish fascia plane out with the underside of the roof deck: mark that spot at both ends of the run, snap a chalk line between them, and set the fascia to the line — dead straight, hiding whatever the framing behind it is doing.
With no truss tails to cut to a line, get dead-straight fascia by setting offset blocks at each end, stretching a line between them, and checking the run with a scrap 2x gauge block — kickers hold what you've straightened.
