Tax treatment may vary 1) from one canton to another 2) if there is an official deemed rental income abroad or not.
Whitout an official deemed rental income, the rental income will be a %-tage of the property value. This deemed income will be considered net of maintenance and repair costs and the tax authorities (e.g Geneva and Vaud) will not allow further deduction.
They are recent case laws from the cantonal and Federal courts on this topic.
Of course, if the property is rented out, expenses will be allowed in the limits of the law.
I’d analyse this option carefully before going further.