Rat poisons and traps are unlikely to control a rat problem in an area with a lot of debris and with accessible places to build nests. You may also want to look in the bookstore under Healthy Home and Environment for books on pest control issues. To-date, I have never found such a design to be necessary or cost effective. While it is undoubtedly true the sloped surfaces shed water more easily than flat surfaces, flat roofs built to standard practices of the trades are reliable and less expensive to build than sloped roofs. Flat roofs do require some greater maintenance than sloped roofs, but their total life cycle costs are still lower than that of sloped roofs.
Flat roofs have some disadvantages.
They are not ideal in areas of heavy snows. They are more difficult to vent. They usually don't allow for easy access to the attic area. It is also important to understand that most flat roofs and roofing surfaces were not built or designed as decks , i.e. walkable surfaces. Inc. All Rights Reserved.