[jstanovic]

Amperage doesn't affect conduit/no conduit. Where it is installed is what's important.
Cables need to be "mechanically protected" in "accessible" areas. Accessible roofspace/underfloor is >600mm.
Mechanical protection also needed up to 2.5m above floor level in gerneral access areas (haven't got access to my rulebook on that one but it's around that).
Attaching a cable to a roof joist/rafter with a suitable clips to prevent sag is classified as mechanical protection, same as under floor.
If there is enough room I would keep the cable under the house rather than into the roof.
6mm cable won't necessarily be on a 32A circuit breaker, run distance/derating factors will determine that. Generally in a domestic situation a 32A circuit breaker on 6mm cable will past testing requirements (including volt drop and loop impedance) up to about 30m, but there are many online calculators to determine that. AS3008 has all the derating factors.
If it was in conduit then you can run it on the angle as shown. Bare cable, no.
If the cable is run is concealed (eg in a wall), needs RCD protection unless it is 50mm away from the finished surface.


If I was you I would conduit it all under the house, that way the sparky can visually inspect it. I've had people run cables for me in roof spaces, never has it turned out well and I have had to redo parts of it. My favourite was the AC circuit someone ran, from one corner of the roof straight to the opposite corner, over all the data cables, AC ducts, plumbing etc. Took me longer to undo it all and redo it properly than doing in from scratch.