Upper case Roman numerals are Major, lower case are minor. Lower case with a degree sign is diminished.
In all Major keys:
We have a lot of choices on how we play [voice] these chords on the guitar. Over time, each of us builds preferences for the way we voice chords. Some chords are easier to finger than others, plus some ring out with certain sound-shapes that we prefer. Also, styles determine the types of voicings we may choose.
One way to apply this list is to play chord scales. This is playing chords alphabetically, ascending and descending, as we play scales.
We also play progressions. We pick a progression such as I-vi-ii-V-I and play it in every key.
7th chords are 4 tone chords. They are taking chord building every other note [EON] until we have 4 tones. We have a root, some type of 3rd, 5th, and 7th.
In a Major key, the 7th type chords are...
I & IV are Major 7 types. The 7 indicated Major 7. You may also see M7 or Maj7. These are Major triads with a Major 7. The Major 7 is an interval of 11 half steps [half step below the root of the chord].
The V is a Dominant 7. It is indicated by just a 7. The V7 is a Major triad with a minor 7. The minor 7 is an interval of 10 half steps [2 half steps below the root of the chord].
The ii, iii, and vi are minor 7. You may also see min7 or -7. These are minor triads with a minor 7.
The vii is minor 7, flat 5. This is a minor triad with a flat 5, and a minor 7. This chord is also known as half-diminished.
The guitar chords in Major keys (triads) are a combination of Major, minor & diminished triads [3 tone chords].
Ideally, after studying guitar for a couple of years, we should be able to play all of these chords in positions where they exist.
There are many many ways to apply this information to the guitar. One is to play chord scales either in a fixed position or a linear sequence, or a mix.
Memorize the guitar chords in Major keys - by quality (Major, minor, diminished), the chords are I, IV, V Major, ii, iii, vi minor, viio diminished. Say it fast, think it slow. Know this.
Diatonic means 'within the key' or 'across the tones of a key center'. A chord not in a key (whether, Major, minor, diminished, or augmented type chords) that is not in a particular family (key) of chords is considered nondiatonic. The Blues are a good example of playing in a key, while using nondiatonic chords [save the V chord].
Play fixed position chord scales.
One of the most advanced things we've discovered is that fixed position alphabetical chord scales follow the cycle of forms (CAGED). Ascending, the cycle goes backwards - DEGAC; descending, the cycle goes forward (CAGED). In both cases, a chord form repeats twice in the cycle, depending on where we are in the cycle and fingerings. This is explored in this article.
Play linear chord scales. Pick a chord form (CAGED) & play the qualities (Major, minor, diminished) up the fretboard, linearly.