Ol' construction type will be pretty much decided by the Building Code Of Aust, But assuming that fire resisting construction is required you will be far better off building in precast or tilt-up concrete panel with a steel portal frame & steel roof.
Are you looking at doing it yourself or via a builder? In rough terms you are probably looking at around $600-750/m2 for the warehouse area, $1000-$1250 for the office space and $150ish for the hardstand areas.
6m wall height is low by current standards as tenants are after as much cubic space as possible ie you are probably needing 8m as a minimum nowadays up to 10 or possibly 12 m depending upon what council will permit. 6 m walls were the norm in the 80's/90's but now with space at a premium height restrictions are much more favourable – you only get one crack at it so go as high as you can (whether you need it or not). Tenants tend to use highbay shelving systems so they prefer as much height as possible for storage – different story if you need it for manufacturing or packaging.
