It is difficult to reconcile the dimentions here with expressions in Zechariah Zechariah 4:10, Haggai Haggai 2:3, and even Ezra Ezra 3:12, which imply that the second temple was smaller than the first (compare 1 Kings 6:2). Perhaps the dimensions here are those which Cyrus required the Jews not to exceed.
Related Commentaries of Ezra 6:3
Ezra 6:3
3 In the first year of Cyrus the king the same Cyrus the king made a decree concerning the house of God at Jerusalem, Let the house be builded, the place where they offered sacrifices, and let the foundations thereof be strongly laid; the height thereof threescore cubits, and the breadth thereof threescore cubits;