Shingles, siding, and gutters — squares and panels from your roof geometry.
A roof is always bigger than the house under it, and pitch is what sets the difference. Estimating from the building footprint is the single most common way a roofing order comes up short — a steep roof can carry substantially more surface than the plan view suggests. These calculators take pitch as an input and apply it, converting between rise-over-run, degrees, and the multiplier that turns footprint into true roof area. Shingles come back in squares because that is how they are sold and quoted. Panels, underlayment, house wrap, and drip edge follow the same geometry, and gutters and downspouts size from the roof area actually draining to them.