When I first started practicing Feng Shui, most of my clients would first buy a house and then use my service to help optimize the interior for them.
In recent years, I see a shift towards first selecting a house before buying and then using my services to optimize the Feng Shui for them.
As a consultant, I highly favor this approach. While both the interior and exterior are important, the surrounding has a more significant effect on the luck of the occupants. The mountain (real and including higher land) and water (real including lower land) in the right places relative to the house can enhance or degrade the Feng Shui quality of the house as well as the spaces within.
For example, a north 2/3 (352.5 to 22.5 degrees) facing house built in the current period of 8 (between 2004 and 2024) should have mountain at the sitting side of the house to enhance the health and relationship quality of the house. And if you decide to use the North East side of the house as a bedroom, it should ideally have a mountain (or higher land) outside at the NE.
Another factor is structure, that generate “Sha Qi” such as high tension pylon that are located nearby the house. Most times it is difficult to block or neutralize such “Sha Qi”. So it makes a lot of sense to buy one located farther away from such structures.
Yet another factor is the the facing direction of the house which can affect the luck of the occupants depending on their Ba Zi. So it makes a lot of sense to buy only those with facing directions that are favorable.
If the house buyer chooses to select before buying, he can avoid all of these problems. He can then concentrate on optimizing the interior, knowing well that the external Feng Shui is fine and supportive.