On large multifamily, commercial and residential buildings, we work outward from the weather barrier: the cladding over it, and the soffit and fascia that close the roof edge. That sentence is the scope, and it is worth reading twice, because most of the arguments on a job happen at its edges.
The layers, from the sheathing out
The weather barrier, lapped shingle-fashion so water runs off it rather than into it.
The cavity, which lets the wall dry and lets water drain to the base.
The flashing at every opening, penetration and change of plane.
The cladding, fixed to stand off the barrier rather than flat against it.
The soffit and fascia at the eave, and the gutter that carries the water away.
Where the scope stops
A package has a boundary, and the boundary should be written down. Ours starts at the sheathing and ends at the gutter. Framing, insulation inside the sheathing, windows themselves and roofing are other trades — and the transitions between those trades are exactly where a leak is blamed on the wrong contractor.
That is the argument for one contractor on the whole outside: when the barrier, the cavity, the flashing and the cladding come from one crew, a call-back has one address.