If you are a perfumer and your intention is to highlight your work, you make the fragrance yourself.
In the other two cases, marketing and budgetary considerations will determine what route you take.
If your budget is limited to a few thousand dollars (or less ... perhaps much less!) and you are not a perfumer, able to make your own perfume, your obvious path is to find a ready-made fragrance oil and turn it into your own brand. This is a simple, inexpensive solution, particularly if you are just starting out with perfume and you want to test the waters.
If an original fragrance is essential for your project and you are not a perfume creator yourself, your solution is to work with a fragrance company that can create a fragrance for you.
Today some fragrance houses may be willing to produce an original fragrance for you for as little as $1,500, depending on your requirements and their work schedules.