The basic forward roll: TM TIM TIM
can be modified to go TIM TM TIM or TIM TIM TM
Each of these variations still has the M strokes striking the 1st string
and the "non-melody" Thumb strokes striking the 5th string.
The odd thing about the easy modification is that the first Thumb stroke can start either
Here is the first line of Bile starting with the regular roll just to get the song started correctly.
Try making up your own variations for the song using these ideas.
If you're thinking of the forward roll as an entire piece to play over a chord, then it's pretty simple to plug in other types of forward rolls.
Here is the second part of Bile using an alternate Forward Roll:
And here is the third line for Mountain Dew:
You can probably figure out the rest of the lines you need from doing this one.
Play around with it. See what sorts of stuff you like.
I like the way the final line gets those low notes to start the next line.
They're in exactly the right place which makes it real easy to sing along with,
Here are some examples using the tuning notes for emphasis.
Again, experimentation on your part will lead to more learning than mere memorization of rolls presented by others.