Establishing the boundary before pricing anything
Rear areas are rarely as simple as the title suggests. A paved strip may be partly on the building's land and partly on a right of way. A bin bay may serve two buildings under an informal arrangement nobody documented. The laneway surface itself is often council responsibility. Walking it with the landlord, and marking on a plan what is included, takes half an hour and prevents a year of ambiguity.
The result should be written in terms a cleaner can act on: to the roller door line, the paved area between the wall and the fence, the bin bay including the enclosure floor. Descriptions like the rear area are useless in practice, because they mean something different to every person reading them. Precision here is worth more than in almost any other part of the scope.
