Q: How do I get better at identifying chords by ear (I, IV, V, etc.)
A: one small thing i could suggest is to stop using roman numerals, because they're just numbers anyway, and those all look too much the same when they keep combining the same 2 letters together. But if that's what you're used to, then that's ok. i'm just guessing that our arabic numberals (1,2,3,4 etc) might be more familiar to you (they certainly are for me). in any case, i would say you should just start going through all the songs you know and working out the chords for them, in any way you can (besides looking them up on the internet, only because that will probably get you the wrong chords), and then over time you will get really really good at it, and start to notice some patterns, then you will see all those patterns break, then if you can keep your head together you will probably start to notice patterns in how the patterns break, then of course you will see those patterns break as well, and then, somewhere around here, it's your turn