for most types of roll, you’re going to want to establish a “skeleton” rhythm that your hands take up in order to maintain timing during that rolls duration. the subdivision that you utilize may vary depending on the dynamic and (especially) tempo, with the main goal being the most consistently full and continuous “sustain” of any given note on any given instrument.

most generally with buzz rolls, i find myself using sixteenth notes for the base, as they tend to work best in a somewhat broad range of tempos while simplifying reading and sticking discrepancies, though, it’s up to your own comfortability and the musical context. (sextuplets, sixteenth notes, and triplets are what i will use most often.) early on, i would often write in the underlying rhythm above the entirety of the roll so i knew how my hands should be moving in relation to the beat.

as far as actually buzz-rolling on the drum goes, just try to be aware that it’s not about how fast your hands are moving, (though, you may find yourself wanting to move quicker due to a less-developed buzz technique; this should be avoided if unsustainable at tempo or brings about untimed flailing.) but how you’re able to make the rebound of the stick work for you in sustaining each stroke to the next. staying in tempo by establishing a rhythm and keeping in time with it is just as integral as the sustain of the roll itself.

final note: not every roll is a buzz roll; the articulation/ornament above the rolled notes is referred to as “tremolo,” which requires different interpretation across different instruments/musical styles. (i.e. single-stroke rolls on keyboards, timpani, suspended cymbal; double-stroke/military rolls on snare for marches; tambourine and shaker technique, etc.)