(Also see "Roof Drainage")
3. Technical: For guidelines on placement and sizing of roof drains, see FM Global's DS 1-54 Roof Loads for New Construction (Data Sheet). You have to sign up in order to view data sheets on the FM Global website, but it's free and definitely worth your time.
4. Technical: Siphonic Drains: "Fundamentals of Siphonic Roof Drainage" is a good introduction to this space-and-material-saving drainage innovation. Available to read on the website of Jay R. Smith Mfg. Co.
5. Manufacturers: You can find roof drain manufacturers here.