So as a bit of a experiment, my groups been looking at how to make a support tank for our Rise of the Runelords game. The goal is to give one or more party members AC and cover. Right now we’ve got a Sacred Shield Paladin going into the Mobile Stronghold feat tree. He's dipping fighter so He'll have it all by 7th level. So right now we’re looking at +10 to party AC from a +5 Tower Shield and total cover on one facing. How do we crank this higher?
You don't? The biggest long term advantage of any shield build is that shields are as cheap as armor to improve with magic.
However, just because armor and shields are cheaper than natural armor and deflection bonus that doesn't mean you neglect the other easy to increase types of AC. Not only is a shield build's maximum possible AC higher, it is more cost efficient than builds that don't use shields...if you spread your gold around evenly. Trying to buy a +5 shield ASAP is a mistake. Someday you'll get a +5 shield, but probably not before you have a +4 ring, +4 necklace, and a +6 dex item.
This isn't about giving the Tank the AC this is about giving other party members +10 or more AC in addition to what they have on them. Sacred Shield already halfs all incoming damage from one enemy. Then he can give his shield bonus to allied standing next to him. The Paladins AC is fine, its already projected to get into the mid to high 30s and climbing. And that's when he isn't untargetable.