Rental income for a room

I have earned rental income from renting out a room in our house. How do I calculate the electricity, rates and taxes (and bond interest) deductible against this income? The room does not have a separate electricity meter, and also keeping in mind that we use prepaid electricity.

Kindly work out the square meterage of the room as a percentage of the square meterage of the whole house, and then apply this ratio to the housing expenses in order to calculate the deduction.