Hey guys.

Say we were to write the roman numeral progression of this one: Em C, Am, F

Is it acceptable to write it as: i-VI- iv- bII? Even though there is no F in the key of E minor?
~Long live the 6-string~
Thats a phrygian progression, so if your implied Key is E Phrygian (relative to C major), then yes, that will work but the bii is redundant in phrygian, just a ii will work. Diatonic Modulation (But nobody cares). But if your implied key is C, that'd be a iii I vii IV, but thats just weird.
just as an fyi you could modulate to any key listed in those chords, C maj, A min or F Major.... i figured you were already aware of this just thought i'd throw in my 2 cents.