Hot take: I just blew $800 on a 'universal' roof hatch that didn't fit anything.
The sales rep swore it would work on our standard 30x30 curb. It was off by a full inch on two sides. Is it better to always custom order, or am I just bad at measuring?
Man, I've been there... measured a curb cut three times and still got it wrong. The problem is those "universal" kits expect a perfect world, and curbs are never perfect. I ended up having a local metal shop bend a piece of aluminum trim to fit the actual gap. Cost a bit more, but it was the only way to get a clean look without weird gaps.
Ugh, that's brutal. I'd say custom order is the only safe bet after a mistake that costly. "Universal" parts are almost never a perfect fit in my experience.