In Fable 3 there is 2 way to do this. One, in front of any buyable house is a sign that you can interact with. Do it to buy the house. Two, the sanctuary or the castle round map table can be used to zoom into any fast-travel area - you can use the magnifying glass to focus on any buyable house within an area to buy it. In any other Fable game you can probably only buy houses with the first way.