Setting up the area is a capital expense, not a tax deductible cost at the time you make the purchase. For income producing property, the capital depreciation rate is set at 2.5% annually.
You can refer to the ATO portal for deductible depreciation items on rental properties, and you will find that certain assets can be claimed over shorter timeframes of 3 to 10 years.
Additionally, a portion of other home expenses such as interest on your mortgage, council rates, and electricity can also be claimed as capital depreciation. Always consult with your tax accountant and, for the most accurate depreciation outcome, engage a quantity surveyor.
Be aware that taking these steps may trigger capital gains tax on the portion of the property used for rental. This can affect long term financial viability.
Another viable option is having a friend or family member stay as a boarder and contribute in cash toward household expenses.
This process is more complex than it appears, so it is essential to get tailored advice from your accountant. I trust this information provides a solid foundation for your next consultation.