I recently ran into the question of phrasing. There was a piece entitled "50 Miles Roundtrip" and I was told that it is supposed to be "50 Mile Roundtrip." I understand that within the context of a sentence "50 mile roundtrip" is correct, but if it is a title, is it still improper to use the phrase "50 Miles Roundtrip?"
Titles can do a lot of things.

If the work is about a drive that someone takes, which is 50 miles in total, "50 Miles Roundtrip" could be fine. But generally, never make yourself crazy over titles - all sorts of liberties are taken by authors.
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Thanks - I was called out by a proofreader who insisted that "miles" is incorrect. But "mile" would be used in the context of a sentence, correct?
I drove 50 miles, roundrip. It was a 50-mile roundtrip.