Containing costs was essential to completion of the project on time and under budget. To economize, the Weston homes and farmhouses were converted into offices wherever possible. The first NAL building was the Linac Research Building, a prefabricated warehouse structure. An "Air Building" was erected and used for prototype work on Main Ring components. Progress on the construction of the accelerator continued, as sections of the site became available. A Master Plan gradually came into focus. The Laboratory's two hundred employees began to depart from Oak Brook and occupy "the Village" in late summer of 1968. Preservation of the land and protection of natural habitats were crucial to these hearty pioneers. The land was formally transferred from the state of Illinois on April 10, 1969.