Would you say "It's too big of a problem"?
No. never say (or write) that! In standard English: too big a problem, too long a journey, too small a payment, too heavy a weight, too big an age gap. Linguists call the use of an additional 'of' the “big of” syndrome.
Kenneth G. Wilson, wrote in The Columbia Guide to Standard American English in 1993, that although “how hard of a job” is nonstandard English, it’s analogous to “how much of a job,” which is “clearly idiomatic and Standard.” Wilson also suggested—two decades ago—that nonstandard “of a” usages “could achieve idiomatic status before too long, despite the objections of many commentators.” Until then, he said, they should be left out of “your Planned and Oratorical speech and your edited English.”
Has that time arrived? Well, these dialectal “of a” usages are becoming acceptable idioms in casual speech and informal writing. However, I still wouldn’t recommend them in formal English, written or spoken. In fact, this dialectal construction—like “how long of a drive”—isn’t found much in print anyway, except in the most casual writing. Fowler’s Modern English Usage (rev. 3rd ed.) calls it an informal oral usage that’s confined, so far, to American English. Merriam-Webster’s says the same: “Our evidence shows the idiom to be almost entirely oral; it is rare in print except in reported speech.”
As M-W concludes: “The only stricture on it suggested by our evidence is that it is a spoken idiom: you will not want to use it much in writing except of the personal kind.” It would be an understatement to call this idiom common in American speech. One linguist has written that for lots of speakers, it’s more than common—it’s preferred.