on :TEXT:!roll:#: {
if ($2- == $null) {
set %dice 1
set %sides 6
%roll = $rand(1,%sides)
msg # Roll 1: %roll
}

Just at a glance, why set a variable if you arent going to use it?
I\'d change the above part to this:

on :TEXT:!roll:#:{
if (!$2-) {
msg # Roll 1: $rand(1,6)
}