Home office space deduction for tax purposes on my ITR12?

You would be able to deduct 10% of the interest and other related costs like insurance, electricity and the domestic and levies/rates. You will need to prove this to SARS so keep a spreadsheet showing these costs and all the actual invoices for the expenses.

Thank you Tim. Will this deduction have an influence when selling the house one day?

Yes it would as you would have to apportion the proceeds/primary residence exclusion.