The rules specify how much damage you take from an object falling on you, but they don't talk about how to dodge said object, or if an attack roll is needed for the falling object to hit you.
All that is stated is that an object does 1d6 for every 10 feet it falls over 20 feet, and does an additional 1d6 damage for every 200 pounds it weighs, while taking 1d6 damage for every 10 feet it falls.
The rules specify how much damage you take from an object falling on you, but they don't talk about how to dodge said object, or if an attack roll is needed for the falling object to hit you.
All that is stated is that an object does 1d6 for every 10 feet it falls over 20 feet, and does an additional 1d6 damage for every 200 pounds it weighs, while taking 1d6 damage for every 10 feet it falls.
Anyone?
Hopefully this is something that will be addressed. Falling damage has come up in the High-level discussion in terms of abuse in combat.
There are a few ways to look at handling it. First is the other 'falling' environment effects, cave-ins and avalanches, which are Reflex save DC 15. That seems to be fairly standard when it comes to "can I dodge that" action.
Another way to 'balance' a falling object if you're building an encounter is to treat it like a trap. For an easy start the base CR will be per 2d6 dice of damage, so a 20d6 damage falling object has a base CR of 10.
Those are two rather easy ways to handle it. You could also use a combination of perception(visual) and a Wisdom check (to judge were it will land) and allow the characters to move, if they have time.