How do you measure a roof?
Measure the footprint with overhangs and multiply by the pitch factor (1 ÷ cos of the pitch) for true area. On complex roofs, figure each plane separately and add hips, valleys and ridges as linear feet.
True area drives shingles, panels, underlayment and cost.
Which roofing should I choose?
Asphalt shingles are the most common and affordable; metal is long-lasting and light; clay and concrete tile are durable and heavy. Each system has a minimum pitch.
Underlayment adds a second water barrier under the roofing.
How are gutters and downspouts sized?
By the roof plan area each gutter collects and your design rainfall intensity: heavier storms need larger gutters and more downspouts. One downspout per 30–40 ft of gutter, and one at every separate run, is a good rule of thumb.
Always discharge at least 4–6 ft away from the foundation or into a storm drain.