Patterson approved the acquisition of the site on 25 November 1942, authorizing $440,000 for the purchase of the site of , all but of which were already owned by the Federal Government. Secretary of Agriculture Claude R. Wickard granted use of some of United States Forest Service land to the War Department "for so long as the military necessity continues". The need for land, for a new road, and later for a right of way for a power line, eventually brought wartime land purchases to , but only $414,971 was spent. Construction was contracted to the M. M. Sundt Company of Tucson, Arizona, with Willard C. Kruger and Associates of Santa Fe, New Mexico, as architect and engineer. Work commenced in December 1942. Groves initially allocated $300,000 for construction, three times Oppenheimer's estimate, with a planned completion date of 15 March 1943. It soon became clear that the scope of Project Y was greater than expected, and by the time Sundt finished on 30 November 1943, over $7 million had been spent.