Would the damage caused by a falling building be qualified as bludgeoning damage?

It would ultimately depend on the nature of the destroyed building, but I'd say that 95% of the damage would be bludgeoning and 5% would be piercing to represent the possibility of being impaled by glass , rebar, broken boards or the like.

Actually, Cave-Ins and similar things are untyped + pin if we go by the traps, crushing if we go by the Iceberg spell and 8d6 bludgeoning + 1d6 untyped every round while pinned if we go by Earthquake.

A DC 25 Strenght check can allow a character to go free. A DC 15 Reflex save either halves or negates the damage Arlong takes.
So the DM needs to be considerate enough to allow the Cave-In interpretation that allows Luffy to live, which is... Well, this is OP, of course he's gonna live...

Well, falling damage isn't technically bludgeoning damage either, but that hasn't stopped his dr from counting for that. It's not energy damage, so unless it was specifically piercing/slashing it shouldn't ignore his dr.

...You mean for this specific case (Luffy), right? Because otherwise you might run into some fairly messed up things when you suddenly turn Hardness to DR and the other way around.

It only just occurred to me that we're getting close to page 1000.

And we're not even out of East Blue yet. At this rate, I don't even think we'll be in Loguetown by page 1000.

Maybe in page 10.000 we manage to see Luffy enter Grand Line

My estimate's gonna be Loguetown by 1015, 1200 for entering the Grand Line, with 1337 being when it's revealed to the Straw Hats that Vivi's a princess.

1337 is quite a precise estimation.
i guess it'll depend if he do the filler before grand Line.