D♭ major has 5 flats (B♭ E♭ A♭ D♭ G♭). Its seven chords are D♭, E♭m, Fm, G♭, A♭, B♭m, C°. Its relative minor is B♭ minor, which uses the same chords with B♭m as home.
On the wheel, IV, I and V sit side by side on the outer ring with ii, vi and iii right below them. Tap any key on the wheel to go to its page.
D♭ A♭ B♭m G♭I V vi IVThe pop engine (Let It Be, Someone Like You)
D♭ B♭m G♭ A♭I vi IV V50s / doo-wop (Stand By Me)
B♭m G♭ D♭ A♭vi IV I VThe same four from the minor side (Zombie, Africa-style)
D♭ G♭ A♭I IV VThree-chord rock, blues and country
E♭m A♭ D♭ii V IThe jazz cadence
D♭ B G♭ D♭I ♭VII IV IRock's borrowed cadence (Hey Jude coda, Sweet Child O' Mine)
D♭ G♭ G♭m D♭I IV iv IThe bittersweet ending (Creep)
Borrowed from the minor
Chords from C♯ minor (how D♭ minor is written in practice) dropped into D♭ major. Rock lives on ♭VII; IV then iv then I is the bittersweet move (Creep).
The same slot on the wheel with a different flavour. Sus chords swap the 3rd for the 2nd or 4th and like to resolve back to the plain chord (D♭sus4 → D♭). add9 adds the 2nd on top of the full chord. These are the common ones whose notes all stay in the key (here: D♭sus2, D♭sus4, D♭add9); the small label is the slot they sit in.
D♭ major: D♭ E♭ F G♭ A♭ B♭ C. The key's seven chords are built from these notes; the borrowed and secondary chords above bring in notes from outside it.