The site grading plan and all construction shall be such that building pads for structures shall drain away at a minimum of 2% grade in all directions from the structure for at least 50' from the edge of structure, unless proper walls, ditches, or underground drainage systems are used to capture and convey 100-year runoff away from the building. In any area in which localized building flooding appears to be a concern, the applicant shall set a minimum finish floor elevation and show such on the grading plans.