This may be a dumb question but I don't understand. If you have a chord progression that starts on a minor or flat chord, how would you write out the roman numerals for it? Or would you just convert the key?
Well that all really depends. For example if you had a minor ii-V-i in C minor then it would be Dm7b5-G7-Cmin7. It just depends on the surrounding chords, not if the chord starts on a minor chord. In a major ii-V-I it starts on a minor chord but it's still in the major key. You really just have to look for patterns in the progression.