Roofing Math: Pitch Multipliers, Roof Squares, Shingle Bundles, Underlayment, Gutters & Quotes

What you'll build

What you will be able to do

Each lab ends with a concrete result that you build yourself and the checker confirms, cell by cell.

• Turn six standard pitches into angles and pitch multipliers, use the multiplier for a rafter length and convert a measured angle back into rise per 12.
• Take Priya's four roof sections from plan dimensions to true sloped area, total them in roofing squares and convert the result into square metres.
• Look up a waste factor for each section's complexity, convert squares into bundles with waste and round the order up to whole bundles before pricing it.
• Give every roof line the right length factor with IFS, total the true lengths and turn them into ridge-cap bundles and drip-edge pieces.
• Work out how much one underlayment roll really covers once the laps are taken off, then count rolls, self-adhesive strip rolls and nail boxes, always rounding up.
• Weigh the old roof from layers and a fictional weight table, convert it into tonnes, decide how many containers the job needs by weight and by volume, and price the disposal.
• Turn drained areas and a fictional design rainfall into flow per gutter run, count the downspouts each run needs and work out the fall over each run's length.
• Price labour per square with a pitch difficulty factor from an approximate-match XLOOKUP, add materials, disposal and overhead, set a price for a target margin and chart the cost build-up.