Identified the left- and right-side flap skins, and marked them with TOP and I/B and O/B just to make sure I don't flip flaps later on (something politicians are prone to do). Also marked the rib locations as #1, 2, 3, 4, 5, and 6, with the inboard locations being #1.

Started building the right flap. After double-checking the level of the bench, I set the skin bottom-side up on the bench with the spar end facing forward. Inserted each rib into position, making sure it was seated properly in the skin and that the centerlines I marked earlier were showing through the holes in the spar. Finger clamped each one into place. All rib flanges face outboard except the #6 rib. Drilled #40 into the two middle holes at the spar end of each rib and clecoed. Then drilled and clecoed the six spar holes toward the top side of the flap (the surface laying on the workbench).

Keeping the bottom skin up, I rotated the flap so the trailing edge was forward. I aligned each rib's centerline mark in the pre-drilled holes of the bottom skin and drilled #40 and clecoed at the trailing edge holes, starting at the middle and working outwards. Continued up the flap, going one horizontal row of holes at a time, until I reached the spar end. Using two levels as lengthwise supports to clear the height of the clecoes, I flipped the flap over and drilled and clecoed the top-side skin in the same fashion. Stopped for the night and cleaned up the work area.