my bold and underline where relevant.
](i) 25 mm over the first 1 m from the building in low rainfall intensity areas for surfaces that are reasonably impermeable (such as concrete or clay paving); or
(ii) 50 mm over the first 1 m from the building in any other case.
If I interpreted correctly, a concrete or paver path need only slope 25mm over 1 metre, so 1 in 40.
A low intensity rainfall area is defined as having an ARI of 125mm or less per hour.