Where have you bought MTM (made-to-measure) suits from?
Online MTM companies are extremely hit-or-miss and you'll usually need to have them tailored locally to be spot on.
Bespoke suits are a whole different animal and are probably what you're talking about when you say custom.
Like anything custom, it's all about the person doing the work.
My personal experience: I'm 5'10" 200 pounds with a larger chest, broad shoulders, large thighs/ass, but a narrow waist (Think fullback style build). I bouce around between 44r and 46r jackets depending on the fit.
Generally, my biggest problems are in the shoulders, chest, thighs, and seat.
Oddly enough, the OTR (Off-the-rack) suits that fit me best are the Lauren (Ralph Lauren) trim fits.
Made to measure is all trial and error- I've gone through 4-5 tailors in the past couple years and still trying to find someone that is affordable and does good work. I can't give you advice on what works, but I can certainly give you advice on what DOESN'T work.
Oddly enough, the best tailor I ever had was also the cheapest. She would alter a full suit for less than $50. Comparatively, the same work from a place like Nordstrom would have cost me around $200 (bring in jacket waist with a large V taper, shorten sleeves, bring in pant waist, shorten inseam, and a full taper of the pant legs).