Estimating, Plans, and Specifications
Squares and slope
Roofing is bid in squares: one square equals 100 sq ft of finished roof surface. The roof plan gives you footprint; you must convert to sloped surface area with a pitch factor: 4:12 gives 1.054, 5:12 gives 1.083, 6:12 gives 1.118, 8:12 gives 1.202, and 12:12 gives 1.414.
Building the takeoff
List every item, not just the field material: starter strip, hip and ridge cap in linear feet, valley metal, underlayment, drip edge, fasteners, sealant, vents, and pipe boots, plus tear-off and disposal. Add waste - roughly 10 percent for shingles, 5 to 10 percent for tile including breakage, and more on cut-up roofs with many hips and valleys.
Reading the documents
Know the drawing set: site plan, floor plan, roof plan, elevations, sections, and details. Drawings give dimensions and layout; specifications govern materials, products, and workmanship. When drawings and specs appear to conflict, submit an RFI rather than guessing or building to whichever is cheaper.
Assembling the price
Material plus labor plus equipment plus disposal plus permits plus overhead plus profit. Labor should come from realistic production rates (squares per crew-day on comparable roofs), not from optimism.
Traps
Using plan area without slope correction, forgetting ridge cap and starter strip, omitting underlayment or flashing from the bid, and performing extra work on a verbal request instead of issuing a written change order.
Worked example: a 40 ft by 30 ft footprint is 1,200 sq ft. At 6:12, multiply by 1.118 for 1,342 sq ft, or 13.4 squares. Add 10 percent waste for 14.8, so order 15 squares plus ridge cap, starter, and drip edge.