1. General: "Roof Drainage - Not My Problem...Maybe" by John Lawson is a very readable although sometimes highly technical article on the necessity of adequate roof drainage and the potential consequences of inadequate drainage. It's available at the Digital Commons section of the California Polytechnic State University website.
2. Codes: The "Roof Drainage" section of the 2012 International Building Code.
3. Codes: The "Roof Drainage" section of the 2012 International Residential Code for One- and Two-Family Dwellings.
4. Codes: The roof-relevant sections of the 2012 International Plumbing Code.
5. Inspection of roof drainage systems: Mastering Roof Inspections: Roof Drainage Systems, Part 1 at the International Association of Certified Home Inspectors' website is worth taking a look at. Part two of this inspection guide can be accessed from this page.