The basic necktie is purchased off the shelf as it were. I see something that will complement my new suit and I buy it.
The step after that is to think about things that are not on the shelf, perhaps in a length that's better suited to my body or a width that agrees with my taste. But that's only the beginning.
The obsessed among us think in terms of pocket squares that complement, but do not match, the necktie. Which may have tipping or a keeper from the same cloth as the suit it's to be worn with. Not to mention compatible braces.
In New York, obsessed men like these have probably already found John Kochis Custom Designs (no web site).
And once they've found Kochis, a man's wishes are the only limitation on the details of the neckties, bow ties, braces, cummerbunds, ascots and scarves he can command, in silk, cotton, linen, cashmere and wool. There are thousands of fabrics from which to choose, and an infinite variety of things that can be made from them.
It's best to have an idea of what one seeks before making an appointment.