Project workflow
Measure the envelope before applying product rules
Establish actual surface geometry
Use sloped roof area for roofing materials and measured exterior elevations for siding instead of relying on floor area shortcuts.
Keep product coverage explicit
Bundle, roll and siding package coverage should come from the selected product; overlap and exposure can reduce usable coverage.
Separate system accessories
Starter, ridge cap, flashing, trim, outlets, hangers and downspouts often need separate takeoffs even when the field material is area-based.