Perimeters is a Riverhead Building Supply showroom featuring windows, doors, cabinets, countertops, hardware and moldings. The Water Mill showroom is a Marvin Design Gallery featuring cabinets from Wood Mode, Medallion, Corsi and Tedd Wood. If you're looking for windows and doors from Anderson, they're at the Perimeters showrooms in East Hampton and Southampton. A design team assists customers and contractors.