Flashing a wood-framed chimney is like flashing a dormer, except there’s no roof behind it. Without protection, water can leak into the joint and rot your walls to direct uphill water away
Just because you draw it doesn't mean they'll build it that way. Know what makes sense, what the framer can execute, and forget about designing in two-foot modules
Peel and stick Z-flashing and some padding pushes a ledger flush with the face of the thick panels. A cover sheet of peel and stick completely waterproof the ledger before the deck is framed