Although the construction may have complied with the standards of the day when the structure was built, many homes we inspect are not built to the current Australian Standards. This is problematic becuase new standards have meant better pratices and things such as tie downs for metal roofs resist them flying away in strong winds (which is common in older roofs)

Whilst. There are no strict building rules for timber framing industry guides such as AS1684 Residential Tim,ber Framed Construction are deemed to satisfy and without any engineer documents to substantiate further, such documents are referenced as items of non compliance in accordance with accepted industry practice. 

The types of defects noted below are very common to buildings older than 10 years old

No straps to halved struts. Where struts are not birdsmouthed or halved to the face they should be strapped, in accordance with AS1684, 
A rafter should not support any additional loads, nor should ceiling joists. Underpurlins should hold up the rafter not vice versa.

Underpurlin spans are generally excessive in older roofs- increased loading one a single rafter at several locations.
Trimming out of openings. All openings should be fully trimmed out with timber supports between rafters/ ceiling joists
Mini collar ties (or straps) to couple the common rafters together at the ridge are required to metal roofs
Tie downs at 1.2m centres are required by the Building Code of Australia 
The spans of the underpurlins are generlaly excessive in older buildings
 

Timber Shrinkage 

Shrinkage to the timbers which is common in hardwood framed roofs. These timbers used to be installed 'unseasoned' or green, which when loaded with weight from roof tiles (in particular) slowly deflect downwards over time. These days roofs are more commonly constructed of seasoned pine. This old construction method presents as an undulating surface from the roof line (or ground) and a slight seperation of the timbers especially at the ridge beam. Common issues related to timber shrinkage are cornice seperation at walls, and beam seperations at the ridge, both occur over time and can be catastrophic to the roof, ceiling frame as well as the ceiling linings.