U.S. lawful permanent residents (green card holders) are subject to U.S. income tax on their worldwide income, regardless of where they live or work. This means they must report all income, including income earned outside the United States, on their U.S. tax return (Form 1040).
if those flats are not rental properties, you do not report them on your income tax return.
further, foreign real estate is not a specified foreign financial asset required to be reported on Form 8938. For example, a personal residence or a rental property does not have to be reported. Ref: IRS Foreign Financial Assets
