What did Cyrus's decree tell the returning exiles to build in Jerusalem?

Answer: The house of the LORD

Cyrus said the LORD had appointed him to build a house for Him at Jerusalem, and invited God's people to go and build it.

““This is what Cyrus king of Persia says: ‘The LORD, the God of heaven, who has given me all the kingdoms of the earth, has appointed me to build a house for Him at Jerusalem in Judah.”— Ezra 1:2 (BSB)