As mentioned before, don't built and buy established. There is no shortage of established homes in Williams Landing for under 600k.
Is this good value when you can buy closer into the CBD at Laverton for a little more than half the price?
http://www.realestate.com.au/property-house-vic-laverton-117675163
http://www.realestate.com.au/property-house-vic-laverton-117482655
A large proportion of listings for Laverton seem to be under offer at the moment even though demographically the area is very poor.