Always roll my sails up; I've found it is worth expirementing as to how to do it.

The Inter 17 sail rolls best when you fold (and I don't like folding modern sails) it at the 3rd batten (having taken the top one out) and then roll top to bottom; I try and ensure that I fold alternate ways and sometimes use 4 batten down. The first Hurricane mainsail was better rolled from the bottom, but my second one was better rolled from 3rd batten down.

Also agree that isa sail is to be stored for a long time, take the battens out.