because I can't play rolls (timps, snares, or other) on a keyboard (maybe it's my premature arthritis?) I draw in lots of little notes into the piano roll on my sequencer (remembering to do left and right hand strikes), and do the following:
(1) apply a script against all the notes to give them a 10% randomness of velocity and timing... this adds an incredibly realistic texture (gone is the "machine-gun effect")
(2) if artistically required, apply relative crescendos/decrescendos over the whole phrase (being careful not to undo the relative random velocities.)
Listen to the following cue from my demos to hear the result... you'll hear timp rolls in second half of the cue, when it gets suspensful.