The 16'x40' addition itself is partially on piers, emerging at L2 of a split.  The floor joist framing – end joists, head joists, ledger, and common joists are laid out as a very large deck would be laid out.

The odd framing at the Northeast corner is to help support a kitchen extension of 3'x12' northward - wall lines included.

Note please the extents to which the AG went to layout a secure pair of raised ceilings, one centered before the zero-clearance fireplace, one center in the bedroom — both centered on finished room dimensions, though we're dealing with roughed.

See how the fireplace and chase must be supported most unusually because it is a decklike floor structure, and we cannot easily rely on a cantilevered structure, i.e., by severing the 3-2"x10" head joists.

The South wall is extensively opened for windows and doors, requiring additional bracing to stabilize it over time — particularly considering the opening and closing of those three big French doors (which will eventually open onto a large exterior deck with spa, planters, and grill.

The broad application of keys eliminates what would have been a welter of notes and leaders obscuring clear visual reference to the drawings themselves.