So you killed a zombie and it got stuck in a pile of rubble or wreckage. Maybe you brought down a house on a few of them. Good riddance.
A day has passed.
Oh boy. There’s that impromptu burial spot again. Wait. What’s making that noise? WHOA! That’s… abnormal.
Slow and extra noisy. These guys are full of debris! Could turn into something nasty if they get the time to mutate. Don’t hurt yourself trying to bring these bumbling resource-ridden monstrosities down. Sharp edges.
I like this idea. I’m imagining something like a skeletal juggernaut but made of rebar and rock.
I would almost accept this over the fact that zombies are currently able to instantly dig themselves out of rubble. At least this provides weird mutation justification.
That being said I’m not sure how lore friendly the zombies incorporating building material into themselves is. It would also be doubly odd when the only thing I dig up from rubble is ash and nails but then I get zeds full of bricks and rebar.
Shouldn’t a roof falling on them sort of… auto pulp them, especially a brick/concrete/rebar roof?
It’d be nice if stuff that dies on top of rubble actually stayed on top instead of phasing underneath the rubble though.
edit: I mean I guess it would depend on the weight of the roof in question
Don’t remember how it works but yeah, it should at least damage them severely.
Kind of the whole point. Not all of them would get up as rubble whatevers. Only the non-pulped ones.
Would also serve as a consequence for taking the “easy” way out. (Other than the loud noises you cause, that is.) Burning a building down or however you choose to do it. I know I’m in the habit of luring a huge bunch of bad guys into regular houses, shutting doors and then lighting the walls on fire as I leave. It tends to work. Not so great when playing with wandering hordes but otherwise it’s a simple solution to a big problem. Too simple.
Punishment.
I don’t really use the burn down house method much myself, when it does happen it’s almost accidental. I’ll be burning out fungals and the zombies will get caught in the cross fire 
I find that the burning house method is very useful when playing with hordes if you want to make any progress moving deep into a city. It kills the zombies inside temporarily and draws all the hordes in the area towards that zone, since collapsing houses are exceptionally loud. Then I just mark that area on my map to remind me never to set foot anywhere within its reality bubble if I can help it, and I move to a different part of town.
Tbh when I think of a roof falling onto someone, I see it as a more like turning something from 3D to 2D.