1. General: Here's an interesting link: the University of Wisconsin-Madison Purchasing Services Division of Business Services publishes their most recent contract for roofing materials and installation services with one of the largest commercial roofing companies in the US with a breakdown by unit price of over 70 items related to the work. Gives you a really good idea of what this stuff actually costs. At least in Wisconsin.
2. General: Price Trends: "Construction Data - Producer Prices and Employment Costs" is over on the website of the Associated General Contractors of America (AGC). "Each month, AGC puts out tables and an explanation showing historical and recent changes in producer price indexes and employment cost indexes for construction materials, building types and subcontractor segments."
3. General: Price Trends: "Producer Price Index (PPI) Detailed Report Information". This is an excellent resource for roofing project cost projection. Once you're on the page, scroll down to where it says "Current edition of the PPI Detailed Report" and click on it. This will open a very large PDF file. To save (a lot) of time, use CTRL-F to search for "roofing". This will return all occurrences of "roofing" in the document, and you can jump from one to the next by using the arrows in the ctrl-f box. You can find price changes (as percentages) year-over-year and month-over-month for production material inputs, finished goods, roofing contractor services by region, and much more. On the website of the Bureau of Labor Statistics, a division of the US Department of Labor.
4. General: A usefully accurate way to find out current material prices is to go to the Home Depot website and search for the item or material you're interested in. If you're using this information to verify roofing estimates, remember that contractors usually get volume discounts on the visible retail price at Home Depot, Lowe's, or any place like that.
5. General: Another good source of current material prices is the GSA Advantage website. Quoting from the GSA (General Services Administration) website: "GSA Advantage!® is the online shopping and ordering system that provides access to thousands of contractors and millions of supplies (products) and services. Anyone may browse on GSA Advantage!® to view and compare the variety of products and services offered." You can search for whatever product you're interested in and get "pre-competed" price results.
6. Low-Slope Roofing: “Factors Impacting Low-Slope Roofing Costs: A National Labor Study” is a detailed 20-page report produced by the CertainTeed Corporation in 2018.
7. Material Prices: General: Best Materials provides prices for a huge assortment of roofing products.
8. Material Prices: General: BuildDirect provides prices for an assortment of roofing products.
9. Material Prices: General: Grainger Industrial Supply provides current prices for a few construction materials.
10. Material Prices: Copper: Basic Copper gives prices for copper nails and copper sheets and rolls.
11. Material Prices: Fasteners: FastenerUSA supplies a variety of construction fasteners and lists their prices.
14. Material Prices: Roof Drains: Josam roof drains* on Amazon.
15. Material Prices: Used Materials: repurposedMATERIALS has prices for used construction materials and equipment. This is kind of a fun site to look through.
16. Material Prices: Ventilation Products: Active Ventilation Products provides prices for a variety of prefabricated items.