Armor Class against CR 20+ creatures

[Nail]

Would you all say that spending about a third (30%) on AC is a typical build?

I've done some calculations based on that premise. Other large fractions of wealth are spent on saves (15%), ability score boosts (20%), and "magic weapons" (anything that helps a PC "attack"; about 30%).

Some of those "top out" at levels 15 - 20, depending on what your DM says about custom magic items. For example, save boosts top out with +5 Cloak of Resistance with just core items.

What's been your experience?

 

[Nail]

If you're a fighter type, take a level of magic-domain cleric and use a scroll of Shapechange. Or UMD it for the rogues. The right forms will get you awsome natural AC, among other things.

nah....Alter Self is really all you need.

 

[Question]

The only way to make yourself unhittable by monsters in that CR range is to make a PC specifically for that. Which will mean hes useless for everything else, and the monster will probably just ignore him and attack the rest of the party.

If we are talking core only, your chances dont look good......you may dodge half the iterative attacks, but the rest will(probably) get you. Why amulet of nat armor is one of the worse items in the game, as it prevents you from using amulet of health. Which is far better.

 

[Garboshnik]

Even if you are still getting hit by big bruisers, larger groups of weaker enemies will probably not have much of a shot at hurting you. This starts to restrict the types of enemies who can reasonably challenge you, which unless your DM adjusts your opponents a lot (I would...) will significantly increase your characters survivability.