Keep detailed records of all the rental income you earn and the expenses you incur. You have to support your purchases and operating expenses with:
Do not send us these records when you file your return. Keep them in case we ask to see them. We may disallow all or part of your expenses if you do not have receipts or other documents to support them.
Generally, you must keep your records for six years from the end of the tax year to which they relate. For more information about keeping records, see Guide RC4409, Keeping Records.