So if measure my body measurements, I presume that the actual shirt measurements will adjust depending on the type of fit of the shirt: regular, slim fit and extra slim fit.
1) So if my bicep is measured at 11 inches, what's the circumference for the bicep area should I expect for the shirt in slim fit or extra slim fit?
2) When measuring my shoulder joint height, it's telling me to leave one finger of space to account for a comfortable fit. So if I measure my shoulder joint height at 7 and half inches. Is that also my shirt measurement or will the shirt maker add more inches so I can actually fit comfortably in the arm pit area?
I think you would be much better off by taking a shirt you own and using those measurements and tweaking them Using body measurements is not a good option to go IMO.