First I divide the population into four age groups under assumption that ages are evenly distributed and life expectancy is 80 yrs. Next, I assume how many % play tennis within each tennis group, finally arriving at "total addressable market". Next I segment these people into 3 segments: rare players, occasional players and frequent players. Based on this (and assuming that avg. # of players in the court is 3) I calculate how many games is played annually. Assuming one game last 1 hour, number of games played annually and hours played are the same. Next step involves making assumption regarding how many hours one court is available per year. Now, dividing total hours played by availability of a court, I arrive at number of courts needed to satisfy total hours played. Final assumption would be that x% of the games (e.g. 50%) are actually played on the same court, splitting this figure in half.

How top-down approach would look like? I might be wrong but I think this bottom-down approach shows better how I approach the problem rather than arrive more easily at some figure which might be more precise..

(edited)