Roofing: ridge, rake/gable, eave/drip, valley, sidewall/endwall
Siding: inside/outside corners, base, J-trim, wainscot transitions
Closures & seal: foam closures, butyl tape, sealants
Wrong inside vs outside closures
Underestimating corner and opening trim
Missing wall-to-roof transitions
Incorrect fastener types/lengths
Forgetting butyl/seal at critical laps