Which suburbs? Green fields are bought by developers and approved for certain lot sizes, the smaller the lots they make an extra hundred million or so. Also because Sydney is forever going west, they are encouraged to do more intense development so the government doesn't need to do even more social and physical infrastructure like hospitals, schools. We've got a real problem with not intensifying our development enough when we needed to in the past so there's huge tracks of suburbs that are considered historical but have excellent ammenities because they are so close to the city but don't have high rises which we realistically need to cater to our population growth. We've not been progressive enough or realistic with our house prices too, there's a lack of units with 3 bedrooms because they don't sell, but they don't sell because they are the same price as a house in an outer suburb and our house prices are so out of control people don't want to make that sacrifice. If you see green, assume it's going to be developed soon in a different stage of land release because they stagger the releases to keep the prices up and if the house is small, again, assume 49 bazillion houses will be around it soon.