How do you do a drum roll?
On a drum staff (a staff set to channel 10) put a base clef and use the note just below the first ledger under the clef (it would be a D). Make the duration 32nd notes and if you want vary them a little so it sounds more realistic
BASS clef!
oops...
How would u do it on a timpani?
With both feet on the floor and holding on to the handrails.
Sorry I'm so late... To do it for a timpani, DO NOT use channel ten use a regular channel, and select timpani from the instrument tab in the staff properties. Use the pitch of the note to select the pitch of the timpany.
Many people also use two different pitches, say a B and a C for a rolling B. I avoid this because it sounds like an out-of-tune timpani to me. I also use a sustain pedal (yes, as is used for piano parts) to help achieve a more realistic sound.
Depending on your soundcard/font, sustain or just plain legato/slur over the repeated notes can make things sound better. Another tip is to accent the first one or two notes in a roll (particularly a loud one) to emphasise the attack. Where there is a roll followed by a rest, or at the end of a piece, you may also have to replace the repeated notes with one or more rests so that the timp. stops playing when everyone else does; this applies to string tremolos also.
>>How do you do a drum roll?<<
Depending on your sound card, one single note can play the whole roll. In my case, it's the F waaaaay down on the staff. Start from the normal F, then go down two octaves. That's where my drum roll is.
As for timpani, I just write what sounds good. I usually use sixteenth triplets, or thirty-seconds.