No grand master plan has ever been found for Filoli but correspondence, records, maps, and drawings help us understand the original design intent. Filoli Architectural Documentation Report Volume 1, by George O. Siekkinen, Senior Architect for the National Trust for Historic Preservation, drew on the research of Timmy Gallagher and Pat O'Brien. Siekkinen also obtained new information from archives and from the Spring Valley Water Company records for his detailed documentation and analysis. From the timeline of the correspondence it is easy to conclude that the vision for Filoli came from its owners and was not the inspiration of a design professional.
The Bourns used a team of artists, consultants and draftsmen to transform their ideas into finished working drawings. It is clear from the research that the master plan was firmly rooted in the minds of the Bourns, and that the house, the garden and the grounds were planned as one unit: the formal garden, starting with the terraces and the sunken garden, following the construction of the house. The entire garden was built spanning the years between 1917 through 1929. The strength of the garden's design is its long links to the house and its compartmentalized character defined by its hedges and walls. It remains remarkably preserved as one of the few surviving and best examples of an English Renaissance style garden. Many of the original 17th century prototypes in England have either been altered as garden styles, have changed, or did not survive wars and years of neglect. Fortunately the Roths respected the original design and maintained its historic integrity for 31 years.
The design of gardens and the grounds is reflected by the personalities of its owners. Bourn's parents landed in San Francisco around 1850. They were leading citizens and members of San Francisco's elite philanthropic society by the time Filoli was built. They preferred a lifestyle of privacy and seclusion and avoided public attention. Even when it came to building Filoli, the project was never publicized in design magazines of the times, as was Harriet Pullman Carolan's estate, Carolands, among others. Mr. Bourn considered that sort of publicity “self-promotion“ and refused several offers. In moving to the country they wanted to get away from the crowds in the city and create a retreat where they would have more leisure time and could have a closer relationship with the land and an opportunity to enjoy nature in all its beauty and serenity. Mr. Bourn was looking forward to “growing young” at Filoli and “being personally involved, for 40 or 50 years, with its supervision.”