Awesome piece. The realistic touches on the roof and the fuel tank give it the character that so much DIY terrain lacks.
A few helpful constructive criticisms -
So this building collapsed, right ? Then why are all the floor boards 100 intact.

I kid, i kid. Seriously though, weathering and splintering the floor boards just a touch would elevate the realism a touch.
Ditto on the broken roof segments - a touch of detritus, rough edges, weathering (a mix of rust and then effectual weathering of whatever caused the damage, so if a bomb / explosion - black carbon scoring ... if just decay, brown / green rust or decay.
Finally on the roof sections everything is very angular. When buildings collapsed, their ceilings droop at the point of collapse even when still nominally attached to the roof. a little bit of angled downward roof sections combined with the dust / grime / cracks / weathering mentioned above would take this to diorama level quality pretty quick.
If you really wanted to get crazy, a couple of scale light fixtures dangling haphazardly from wire, and some scale realistic graffitti would be great too.
All just nitpicky
CC'ing, the piece looks wonderful as it is - it's lightyears above most DIY ruined buildings.