Perhaps you already realize this, but I think the trick here is: You want to ask soon enough to avoid wasting your time and the company's time pursuing an opportunity that you're going to reject, but on the other hand you don't want to give the impression that you are demanding, that you care more about office amenities than you do about producing for the company.
(Even if that is, in fact, entirely true. I was on some forum, maybe this one, maybe another one, where someone said that when applying for a job you don't want to give the impression that you put a high priority on how much they'll pay you. Well, duh, I certainly DO put a very high priority on salary. And I'd think that the interviewer cares a lot about how much his salary is, and if he doesn't realize that I care too, he's an idiot. But you're not allowed to say that. One of those bizarre social rules: we all know it's true, but you're a social pariah if you say it out loud.)
No one can give a definitive answer, like "bring this up 42 minutes and 15 seconds into the interview". But it's a matter of balance. I certainly would not make that the first thing I brought up. But if the company has a long interview process, I wouldn't wait until after we'd gone through days of interviews either. If this is really a deal-breaker for you, then it's something that is probably a rather straightforward question. I mean, there are things about a job that are very subjective, where you have to consider what they told you and think about how they might have slanted it, etc. A question like, "Would I have a cubicle or a private office?" is simple and straightforward.
So I'd first ask questions about the nature of the job, what kind of work I'd be doing, etc, and then after I'd asked a number of those sort of questions, ask to see the office space, or if for whatever reason that's not possible, ask questions about it.
By the way, just as a matter of politeness, I wouldn't say, "I won't take the job unless I have a private office with big windows." I'd make it a question. "Would I have a private office?" etc. That just sounds more polite.