Muller moved on to the firm of D. Everett Waid in 1912 where he was also employed as an architectural designer until 1914, when he opened his own office in New York City.
[3] Muller’s earliest known work in South Florida dates to 1923 when he designed a number of Mediterranean and Spanish-style houses in the Miami area.
Later, they met at the site that was to become Opa-Locka, where Muller described his concept for the city’s architectural design, derived from the individual stories of the Arabian Nights.
[3] In 1942, Muller retired from full-time practice, closed his office, and went to work for George M. Sharp, Inc., as the interior designer for luxury ocean liners.
The American Architect Directory of 1956 lists his most notable designs for these churches as those in Brooklyn (1918), Hempstead (1924), Forest Hills (1925), Bronxville (1929), and Flushing (1930), all in New York, as well a building for a new congregation in Opa-Locka (1930).
According to Frank S. Bush, a friend of Muller’s, he was known as a man of great foresight, unimpeachable reputation and integrity, in addition to being thoughtfully creative.
In an interview with Opa-Locka’s newspaper, the North Dade Hub, Muller explained the original intent of his scheme for Opa-Locka:[3] In planning the city, our [Muller and Curtiss] idea was to avoid the only too-well known checkerboard idea of development with the visual square boxes planted on each lot, making a composite of architectural abortions with which we are surrounded on all sides in America.
In addition to many altered and demolished buildings of his design, he found a collection of plain, unappealing structures, much like any other American town could exhibit, which he sought to avoid in his work.
[3] Muller left Opa-Locka, the city of his dreams ruined; he returned to Short Hills, New Jersey, where he continued his architectural practice until about 1962.