If you have a RTW dress or sports shirt that you like but is large across the chest and waist, here's a Threadbanger (what a name!) DIY video on altering a shirt by taking in the sides:
Remember pinch and pin, pinch and pin and sew. Obviously, I wouldn't recommend this for your $600 Anna Matuozzo shirt. But as the video suggests, if you are serious about making shirts, there is a very good book called Shirtmaking by David Page Coffin, which my own shirtmaker Freddy Vandescasteele recommends.
The video also features Bodymetrics, a body measurement company. Bodymetrics is focused on using its bodyscan for fitting jeans (apparently 25-30% of all garments are returned due to wrong size).
A cheaper alternative to Bodymetrics is creating a bodyform using three tools - a duct tape, a t-shirt and a friend. Seems much more commonplace in constructing women's clothes. It would be interesting to know of any men's tailors or shirtmakers who take this approach.
by David Page Coffin, which my own shirtmaker Freddy Vandescasteele recommends.