I've been estimating roofs for over a decade. Here are the real variables I see driving cost up or down on every job I bid.
1
Roof size (square footage) — Every estimate starts here. Roof area isn't your home's floor plan — it's the sloped surface. A 2,000 sq ft ranch has roughly 2,000 sq ft of roof. The same house with a steep gable can push 2,400+.
2
Pitch / steepness — Anything above a 7/12 pitch requires harness gear, toe boards, and slower work. I add 15–35% to labor the moment I see a steep slope. A flat roof is the cheapest to walk.
3
Number of existing layers — Two layers of old shingles mean more tear-off labor and higher dumpster fees. Some codes only allow two layers total; after that you're ripping to the deck regardless.
4
Material choice — Asphalt is the baseline. Metal costs 2–3x because the panels are custom-cut and the labor is specialized. Slate is heaviest — your roof structure may need reinforcement before a single tile goes on.
5
Underlayment grade — Felt paper is cheap. Synthetic underlayment costs more but lasts longer if the roof sits exposed during a slow install. Ice-and-water shield around valleys and eaves adds $200–$600 per job.
6
Flashing condition — Step flashing around chimneys and walls is often rusted or mismatched. Replacing it is a few hundred dollars. Skipping it causes leaks that cost thousands later.
7
Penetrations (chimneys, skylights, vents) — Every hole in the roof is a leak risk. More penetrations mean more flashing, more caulk, and more time. A simple roof with two plumbing vents is cheaper than one with four skylights and a chimney.
8
Accessibility — Can my crew park a dumpster within 20 feet of the work area? If not, we're carrying shingles and tear-off by hand. That adds 10–15% to labor. Second-story roofs with landscaping below also slow things down.
9
Region and local labor rates — A roofer in rural Alabama charges different money than one in San Francisco. Our calculator's regional multiplier (0.85x to 1.30x) reflects the real spread in prevailing wages.
10
Seasonality — Summer is peak roofing season. If you book in October or March, you might get a discount because crews need work. Winter tear-offs in cold climates cost more — ice and snow slow everything.
11
Permit fees — Not all jurisdictions require a permit for re-roofing, but many do. Fees range from $50 to $500. Some cities also require an inspection, which adds scheduling overhead.
12
Disposal and dumpster fees — A standard roof tear-off fills a 20-yard dumpster. Disposal fees vary by landfill — $200 in a rural area can be $600 near a metro. This is a line item I always call out separately.
13
Warranty tier — Manufacturer warranties (30-year, 50-year, lifetime) cost more upfront. Workmanship warranties from the contractor also add cost. A "lifetime" shingle might cost $10–20 more per square than a 3-tab budget shingle.