What fall on tiled alfresco?

I assume you meant 30mm step down from the house slab. If not make sure you have adequate step down to outside area so you don’t get stormwater inside house.

Please see below from the BCA.

Surface drainage
Section 3.1.2.3 of the BCA states:
‘Surface water must be diverted away from Class 1 buildings as follows:
(a) Slab-on-ground — finished ground level adjacent to buildings:
the external finished surface surrounding the slab must be drained to move surface water away from the building and graded to give a slope of not less than (see Figure 3.1.2.2);
(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.
(b) Slab-on-ground — finished slab heights:
the height of the slab-on-ground above external finished surfaces must be not less than (see Figure 3.1.2.2);
(i) 100 mm above the finished ground level in low rainfall intensity areas or
sandy, well-drained areas; or
(ii) 50 mm above impermeable (paved or concreted areas) that slope away from
the building in accordance with (a); or
(iii) 150 mm in any other case.

A gap will direct stormwater under the house foundation which could cause movement and building cracks.

It’s not recommended and it’s non-compliance with building code to have the outside slab level similar to house slab as it’s potentially could direct stormwater to inside the house.

The code as mentioned require at least 50mm step down with a slope away in the exterior slab as previously stated.

As mentioned, it’s not recommended to level the outside with inside slab. It’s also recommended to fill any gaps between outside slab and building with flexible sealant to avoid any water ingress and future movements.