Before specifically.
שו"ע א"ח תרצ:יז says clearly to roll it up first and then make the ברכה.
מ"ב ס"ק מז says דגנאי הוא למגילה שתהיה מונחת כך.
If you're trying to say that minhag Chabad is to do it before (which, of course, it is), say so explicitly. Especially since the one that asked the question is not Chabad.