Single family ranch extension

Existing ranch house at 19 Fraternity Lane, Stony Brook, NY on 100 by 150 lot. Seeking to add large handicapped accessible addition with three bedrooms, 2 1/2 baths and two small living areas for extended family. Addition to create L shaped structure with no need for second kitchen and/or mother-daughter conversion. Full basement required for storage. Town of Brookhaven zoning limits may be 7 1/2 ft. setback and 18 ft. height. Existing pool and gazebo may or may not limit buildable area as a percent of side and backyard area [25% ??]. Total project budget $200 to $300k