Tower shields kind of suck...hard. Just use a heavy shield instead.
The cover only happens if you use a standard action to place the shield. And it only provides it to 1 side of your square (out of the 4). You also cannot perform a shield bash with it, and you take a penalty to all attack rolls because of it.
Shield, Tower: This massive wooden shield is nearly as tall as you are. In most situations, it provides the indicated shield bonus to your AC. As a standard action, however, you can use a tower shield to grant you total cover until the beginning of your next turn. When using a tower shield in this way, you must choose one edge of your space. That edge is treated as a solid wall for attacks targeting you only. You gain total cover for attacks that pass through this edge and no cover for attacks that do not pass through this edge (see Combat). The shield does not, however, provide cover against targeted spells; a spellcaster can cast a spell on you by targeting the shield you are holding. You cannot bash with a tower shield, nor can you use your shield hand for anything else.
When employing a tower shield in combat, you take a –2 penalty on attack rolls because of the shield's encumbrance.
Tower shield are terrible and not worth the +2 AC versus a heavy shield, and there are much better way to spend you standard action than to attempt to grant yourself cover that is negated by someone simply 5ft step around your square. Not to mention the cover doesn't even protect you from spells, which are far more dangerous than weapons.
Tower shields are awful in terms of mechanics.
Take a heavy shield. Pick up the shield bashing feats.
If the flavor is important, describe it as a big tower shield, but mechanically it's a heavy shield.
I personally have never used a tower shield so i didnt know about the drawbacks nor have i ever had anyone want to use one.
Well know you know exactly why no one does. Mechanically they're just terrible in the game.
The only person that can use them sort of well is the Tower Shield Specialist Fighter Archetype. However, that is rarely used because you lose Weapon Training which is really the only good thing the class has going for it in the first place.
Definitely discuss it with them and see if they're set on the crunch of the tower shield, of if they can deal with a standard sword and board paladin.