Rule 16 Tower Shields: How the #&%@ do they work?
At the start of their turn, a creature using a Tower Shield decides whether to use the Total Cover version of their shield, or whether to use it for a shield bonus. This is a free action. Tower Shields being used to provide Total Cover provide cover in all directions. You cannot make any Attacks*, as defined by the Glossery, while using a Tower Shield to gain cover. Actions which do not provide an attack roll are not attacks, and may be used while a tower shield is providing cover.
*Any of numerous actions intended to harm, disable, or neutralize an opponent. The outcome of an attack is determined by an attack roll.