I was wondering if I could use his ability to make my creatures attack on an opponent's turn
{Boros Battleshaper}
No. Only the active player may declare an attack.
506.2. (http://imtgapp.com/forum/index.php?action=imtg;area=rule;number=506.2.): During the combat phase, the active player is the attacking player; creatures that player controls may attack. During the combat phase of a two-player game, the nonactive player is the defending player; that player and planeswalkers he or she controls may be attacked.
Ok thanks key!