The ADA requires that all new construction of places of public accommodation, as well as of "commercial facilities" such as office buildings, be accessible. Elevators are generally not required in facilities under three stories or with fewer than 3,000 square feet per floor, unless the building is a shopping center or mall; the professional office of a health care provider; a terminal, depot, or other public transit station; or an airport passenger terminal. The 2010 ADA Standards for Accessible Design set minimum requirements – both scoping and technical -- for newly designed and constructed or altered public accommodations and commercial facilities to be readily accessible to and usable by individuals with disabilities.
See the 2010 ADA Standards for Accessible Design for more information regarding new construction: https://www.ada.gov/regs2010/2010ADAStandards/2010ADAstandards.htm
For additional information, take a look at the following resources: