[onewhippedpuppy]

The "contractor grade" crappy wood windows in my house were all shot, we went with exterior clad Andersen windows and had the same issue with custom sizes. We were able to go marginally smaller or bigger by an inch or two depending on the windows and use their stock sizes, which saved thousands. To compensate we had to replace the interior trim with slightly wider (which looks better anyway), and custom rip the exterior trim to fit.

Andersen makes fantastic windows, my father in law is a contractor and has been installing them for 30+ years. Very rarely does he have a callback, and when he does their warranty is excellent.