there are a couple of floors in your rent a room out theory,
they are
if everyone rented out 1 room to buy a house, would there then be no demand for rentals and just heaps of supply?
in which case -) you wont get your high rent -) you will have problems renting out that room
Also if you have children, or a wife that looks after the kid(s) your not going to find it easy at all getting a loan for $400K, and you have to rent that room out imeadiatly, if everyones doing it thats going to be hard to do and the rents will drop.
dont forget, this is not a solution for just a few people or your mates, this has to be the solution for the average Australian. and it has to be sustainable to maintain the property prices and keep holding it there.
and have you ever tried living on $300 a week? i know i wouldnt want to! no way would i have any money to save for a house in that situation to progress from renter to buyer..
