Roofing, siding and rainwater

Shingles and metal panels by square, with underlayment, ridge cap, fixings and the ice-and-water membrane at the eaves; pitch and squares converted both ways; lap siding, board-and-batten and house wrap; and the gutter, hangers, fascia, soffit and downspout that catch what comes off.

The pitch, and it decides more than the covering. A slope is longer than the plan under it — half as much again at 45° — so a figure taken off a footprint is short before anything else is considered, and the same pitch sets the underlayment overlap, whether a starter course is doubled, and how far up a valley the membrane has to run.

Flat and low-slope work, whose membranes and falls are a different trade, and the structure the covering is fixed to.