when did the construction of this place first begin?
14 September 1948.
Headquarters of the United Nations

The groundbreaking ceremony for the initial buildings occurred on September 14, 1948. 
where is the headquaters of the united nation situated New York City . who is the design of this headquarters attributed to? A board of architects led by Wallace Harrison. where is this person from? United states of America. and what was he by profession? An architect. was the headquarters situated at an earlier place before? Yes, there were a number of temporary sites where this was located.
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Headquarters of the United Nations [SEP] Construction
The headquarters were originally supposed to be completed in 1951, with the first occupants moving into the Secretariat Building in 1950. However, in November, New York City's construction coordinator Robert Moses reported that construction was two months behind schedule. By that time, 60% of the headquarters' site had been excavated. The same month, the United Nations General Assembly unanimously voted to formally thank the national, state, and city governments for their role in building the headquarters. The formal $23.8 million contract for the Secretariat Building was awarded in January 1949. A prayer space for people of all religions was announced on April 18, 1949.