Size categories for improvised weapons?

[ZenBear]

If a man throws a mug at you, I can see 1d4+STR, but when a Giant throws his chair? Or a Tarrasque throws a house? How would you rule the damage on that?

[Wartex1]

I'd improvise it. A ball and chain would be like being hit with a warhammer or maul (though damage is silly when a mug can do a good fraction of the damage of a ball and chain). A house might be anywhere from 3d6+10 (say, a flimsy wooden shack) to 10d10+30 (a sturdy, brick home).

[sengmeng]

Complete adventurer has the rules for this. It's based on weight and hardness/sharpness. Basically you have to know the weight of the object.

Edit: sorry, complete warrior. Page 159. 400 pound items deal 5d6 damage, +1d6 per 200 lbs beyond that.