MUMBAI (AFP) - India's richest man Mukesh Ambani faces a possible federal probe into the construction of his 27-storey luxury home -- one of the most expensive private residences in the world. The Maharashtra state government is considering whether federal investigators should look into alleged irregularities over the sale of the land on which the home was built, Indian media reported on Tuesday. The Reliance Industries chairman, who according to Forbes magazine is the world's ninth richest man with a $27-billion fortune, moved into the 570-foot (174-metre) tower last year.