A few things could cause dry rolls. Overbaking is a common culprit, so keep an eye on them in the oven. Also, adding too much flour to the dough can make them dry. Remember, the dough should be slightly tacky, not completely dry. If you live in a dry climate, you might need to use less flour than the recipe calls for. If you live at a high altitude, consult this article on adjusting the recipe.