Who is landmark construction group? Landmark Construction Group, LLC is an Oklahoma City based construction company active in the commercial building industry throughout the State of Oklahoma. As a commercial contractor, Landmark does work in both the private and public construction sectors.How do i contact landmark customer service? For customer service support, visit our Customer Service Page. Comments and Inquiries If you have a question or comment that is not addressed on this Web site or by your local center, please write to Landmark, Attn: Harry Rosenberg, 353 Sacramento Street, Suite 200, San Francisco, CA 94111.How do i get in touch with landmark education? Customer Service and General Inquiries. Contact your local Landmark office. Schedules and Available Programs in Your Area. See course schedules. Corporate Headquarters. Landmark. 353 Sacramento St., Ste. 200. San Francisco, CA 94111. Phone: 1-415-981-8850.Does landmark work in the private and public construction sectors? As a commercial contractor, Landmark does work in both the private and public construction sectors. Our portfolio reflects a persity of projects acquired both by working directly with our clients in the private industry and competitively bidding on public works projects.