This is a great market sizing question.
Now, I would turn to you and ask: Are you more comfortable with the top-down or the bottom-up approach here?
There is no right answer. The answer depends on how good of a grasp you have on the numbers/estiamtes required, and how comfortable you are with the logic required in each case.
In this, case a good top down might be:
- Measure the US economy (~20 trillion).
- Then, estimate what % of this NYC accounts for
- Either a hard # if you know it or,
- A state number of you know it (then a city estimate) or,
- A "all cities" vs "rest of country" estimate, then break down further
- Take that % and do a NPV on that recurring GDP contribution (with growth/discount factors accounted for)
A good bottom-up might be:
- Estimate the value of residential, commercial, and industrial buildings/activity in each of the 5 buroughs and add them up
Which do you feel more comfortable with? Or, has this prompted you to think about the question another way?