I buy my dress shirts at Indochino. They do multiple first measurements on you the first time, then they make a first iteration shirt. You come for a second fitting with that shirt when they look how it sits and re-adjust the measurements which are stored in your profile and all subsequent shirts are made to them. The result is pretty good. Never been to a custom tailor but I guess this is a good industrialized approximation of what they do. I am wondering if something like this could have worked.