Manfredi was mainly responsible for the dome and the roof of the building, which was designed in the Italian Renaissance and neoclassical styles and modelled in part after the Basilica of Superga. "Much of that copper covering the Hall, I put on with my own hands," he said in an interview with the "Bangkok Post" in 1967. He also contributed to the decorations and was responsible for later work on the building's foundations. He acted as chief architect for Mrigadayavan Palace in Cha-am and was in charge of its construction, which took place from 1923 to 1924. Designs for the seaside villa were sketched by King Vajiravudh and implemented by Manfredi. The palace consists of sixteen buildings and incorporates the Thai manner of elevated buildings with Western style and details. He also contributed to the design and construction of Villa Norasingh (1923–25), now the Thai Khu Fa Building of the Government House, although it is not officially attributed to him. The building was constructed mainly in the Venetian Gothic style and has a façade resembling that of Venice's Ca' d'Oro. He was not satisfied with the results, saying in a 1967 interview, "I built it in the Venetian style because I thought that Bangkok was the Venice of the East. Now I am so ashamed of it. It is not just right for this climate." Manfredi produced many modernist designs in the 1930s. These include Manfredi Residence (1935) and Asawin Villa (c.1930s), which were influenced by the Bauhaus school and are among the first modernist buildings in Thailand. The decade saw widespread adoption of the International style for public and educational institutions. Among these are Manfredi's designs for the Rajvithi School of Nursing (c.1930s) and the Chulalongkorn University Faculty of Dentistry (1939). Influences by the neoplastic (De Stijl) movement are seen in his designs for Triam Udom Suksa School (1934). He also designed Chulalongkorn University's Faculty of Fine Arts building, as well as the Chemistry and Physics buildings of the Faculty of Science. Other contributions by Manfredi include:   Manfredi did not specialise in sculpture, but two such works by him are known. They are the marble guardian lions at Wat Benchamabophit and the statue of Jarlet, King Vajiravudh's beloved dog, at Sanam Chandra Palace.