Hi Andrew Family
The stamp duty in SA is paid by both permanent and temporary residents on the purchase of a property. If someone were to buy land to build a home the stamp duty is only payable on the land thus reducing it by quite a bit.
The FHOG is only payable to permanent residents (http://www.revenuesa.sa.gov.au/fhog/index.html) and is capped at $575,000.
There may also be eligiblity for the First Home Bonus Grant (FHBG) if building of up to $4,000 (caps to land/build price apply).
If someone obtains permanent residency 12 months after purchase/build then the grants may be able to be claimed retrospectively.