(Also see "Roof Drainage")
1. Building Codes: "1503.4.2 Scuppers" and "(P) 1503.4.1 Secondary (emergency overflow) drains or scuppers" in the 2015 International Building Code. Available on the UpCodes website.
2. Building Codes: "R903.4.1 Secondary (Emergency Overflow) Drains or Scuppers" from the 2015 International Residential Code. Also note exception 2 under subsection 1 under "Section R908 Reroofing". Available on the UpCodes website.
3. Technical: An excellent technical article on scuppers is available here at the website of the Copper Development Association. Provides construction details for various scupper types. They talk about scuppers being made out of copper in that article, but that doesn't mean that scuppers have to be made out of copper or that the information provided is only applicable to copper scuppers. (Copper is a great scupper material, though).