Building codes don`t require bathrooms to have a window, but natural ventilation is best. If you have to rely on an extractor fan for ventilation, make sure it ducts outside of the house rather than into a ceiling cavity.
Pay particular attention to the waterproofing membrane that goes underneath tiles around a shower area to stop water permeating the walls and floors. This is not something that you want to get wrong.
Beware of selecting large tiles, especially if you want to use them on the floor. Bathroom floors need to slope towards a central drain, and large tiles often need unsightly triangular cuts to be laid correctly.
Shower screens, bathroom and toilet doors need to open outwards, in case someone collapses in a bathroom and falls in front of a door.
The Australian Government has implemented new water-efficient plumbing guidelines that prohibit retailers from selling water-guzzling taps, toilets and showerheads. Check www.waterrating.com.au for details.