I am not sure of identification from 5-6cm length plus this photo. Near buildings it is likely to be a Black Rat, Rattus rattus and at that size would be juvenile. But they do not live far out in short mown grassland like this location. Maybe it has wandered there in response to been poisoned in the buildings? Do you have other photos or did you keep it (for biosecurity reasons in case it had travelled here in an aeroplane)?
I've got a couple more pics, both side on. One shows body - no tail visible. The other shows tail - head obscured. I didn't keep it. Initially found it using a thermal scope.