Matthew Poole and continuators on 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 built, 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 :

He did not command them to make it so large, for he left the ordering of the proportions of the Building to their skill and choice; but he restrained them that they should make it no larger; lest they should hereafter make use of it to other purposes against himself: But those proportions differ much from those of Solomon's Temple, which was but Thirty Cubits high, only the porch was 120 Cubits high, and but 20 Cubits in breadth. Either therefore Solomons Cubits were sacred Cubits, which were larger than the other, and these were but common Cubits. Or, the 60 Cubits of heighth are meant only of the Porch, which he would not have to be so high and magnificent as that of Solomons was, lest they should be puffed up with it, and by degrees arrive at their former heighth and insolence. And the word rendred, breadth, may be, and is by some rendred more generally, the extension, or amplitude, or the length of it; it being improbable that the King should give orders about the breadth and none about the length of it.