Hi All
The following link from the ATO helps answer this more clearly
http://www.ato.gov.au/businesses/con...&mfp=&st=&cy=1
But overall, whatever method you use to claim you must be able to justify it. Doesn't have to be floor space % only. As long as you can justify/explain what your claiming and why you've picked the proportion/allocation you have.
A lot of accountants advise not to claim anything but occupancy expenses such as electricity and internet (apportioned) due to Capital Gains consequences later down the track.
Fletcher Tax Accountants
www.fletchertaxaccountants.com.au