Unless I am mistaken, stratum is the singular of strata and refers to a layer of the building, in this case the entire ground floor area.
But your neighbour has a five-storey-high flagpole? I hope the owner knows that they have to take an Australian flag down at night or, by law, ensure it is illuminated.
And I would imagine your neighbours would object to bright lights shining in their windows all night so the flag would have to be lowered every night.