Koesari Ratmono is responsible for design development, project management and construction documentation and implementation for a diverse range of Belt Collins' hotel, resort, residential and commercial projects throughout China and Southeast Asia. His key knowledge is hardscape design, material selection and construction detailing, coupled with site work. He has been involved in projects from initial site visits and throughout the design process.

Koesari leads the Bali office in providing local coordination and design support for Belt Collins Singapore's projects in Bali and throughout Indonesia.