I'm a drummer, so I'll give it a try. Actually, it's not that hard to make a tom rolls. Take 2 or three toms. One hi tom, one mid tom and one low tom. Pan the toms so that the hi tom is more to the left (not totally to the left, just a tad) the low should be to the right (same thing... just a tad) and the mid can be kept in the center.
Now, for the toms placement, they are mostly used to make breaks, even if you can put them else where and use them as percussions (like bongos and the such)... now, the thing is, there is no real rule to place the toms, but here's what I could suggest:
(H: HI TOM M: MID TOM L: LOW TOM S: Snare)
The easiest tom roll is :
- - - - - - - - - - H H M M L L
and you can start the next pattern with a cymbal
or
S S S S H H H H M M M M L L L L (with the cymbal...)
If you want to have a more natural sound, you can also change the velocity of each hits like so...
S s s s H h H h M m M m L L L L (with the cymbal...) (S for Snare)
then you can always make it so your tom placement accompany your beat... as for anything else, experiment makes perfect!!!