As an idea:
Suppose you have a nice shirt, T-shirt or other piece of clothes which fits perfectly.
Is there a way to reliably determine (some of, depending on the piece you disassembled) the freesewing-measurement set data from that piece? Especially the shoulder-slope and waist-to-armpit data is quite difficult to measure on the body, perhaps easier from a disassembled shirt or sweat shirt or hoodie or the like.
Reliably? No. I means you could disassemble the shirt and simply measure the angle of the shoulder seam in the front and back part, take the average if they differ, and that gives you the shoulder slope they assumed when designing that garment. But that’s very likely not the shoulder slope of the wearer.
There are smartphone apps to measure angles based on the phone sensors.
You can also use paperless view to compare the dimensions of a pattern to the garment you have and adjust options and measurements until it matches, if your goal is to clone that piece.