Be sure to roll the cake in a generously powdered sugar-dusted kitchen towel while the cake is still warm from the oven. This sets the shape of the cake in a roll shape prior to adding the filling and makes it much less likely to crack when you roll it back up with the filling inside. Some recipes call for vegetable oil instead of melted butter which may make your cake more pliant (but sacrifices the buttery flavor). As long as you roll the cake in the towel while it is warm, you should be fine.