I've only used two shirtmakers, so I can only offer comments based on my limited experience. I was using Mel Gambert (I think they are based on NJ, and I also believe that their shirts are produced in-house. I can't comment on if this is truly bespoke with individual patterns, but their customizations seemed fairly extensive). The quality and fit of the Gambert shirts was pretty good, but their turn-around time was atrocious. I'm now using Turnbull & Asser, and I do believe that they produce individual patterns. I can't really say what they are willing to modify, as I only made a few tweaks to the sample shirt, as the fit was almost perfect. Their turnaround time has always been in the 3-week range for all of my orders, which I think is pretty good coming from the UK and then stopping through the NYC store before being forwarded to me. The bespoke manager at T&A did mention to me that Charvet is also another bespoke option in NYC (in addition to Ascot Chang which was previously mentioned), but I have no first-hand knowledge of them.