Building rubble -- red-brick + browns & greys. Sectons of building would be Brick-red, cream stucco, then off-white for the stone window surrounds. In comparison, that 44-gallon drum looks huge beside that window frame !
Cobble-stones are various shades of grey + dark grey wash between.
Lots of work but you need to paint each stone individually
Some dry-brushing brings it up nicely too.