A roll is another name for an arpeggio. So, basically just take your chord(s) and play each note one at a time, holding down previous notes. Start slow then increase speed as your fingers gain accuracy. Practicing rolling/arpeggiating the chord fowards and backwards. Start with this chord for practice:
AbM7= Ab-C-Eb-G
foward: Ab(hold), C(hold), Eb(hold), G(hold) REPEAT
backward: G(hold), Eb(hold), C(hold), Ab(hold) REPEAT
Like I said, start off playing it slow, then gradually increase the speed. Once you can do it good in one spot, practice arpeggiating over 2 octaves forwards and backwards. Then 3 octaves, 4octaves, etc. until it becomes second nature.
After you can do this for a chord in root position, next try doing the chord inversions:
AbM7= Ab-C-Eb-G (root position), C-Eb-G-Ab (1st inv.), Eb-G-Ab-C (2nd inv.), G-Ab-C-Eb (3rd inv.)
foward: Ab(hold), C(hold), Eb(hold), G(hold) REPEAT
C(hold), Eb(hold), G(hold), Ab(hold) REPEAT
Eb(hold),G(hold),Ab(hold),C(hold) REPEAT
G(hold), Ab(hold), C(hold), Eb(hold) REPEAT
backward: G(hold), Eb(hold), C(hold), Ab(hold) REPEAT
Eb(hold), C(hold), Ab(hold), G(hold) REPEAT
C(hold), Ab(hold), G(hold), Eb(hold) REPEAT
Ab(hold), G(hold), Eb(hold), C(hold) REPEAT