I built my first home with Ausbuild around 2 years ago. As any first-time build, it was a daunting experience due to my lack of knowledge of the process.
In the end I got my house, not quite on time, 6 weeks later than expected, but the build quality was 'below average' according to my independent building inspector. There were some structural issues that could have been rectified easily during the build if Ausbuild took more care with it. While none of the issues breached building standards, they were sloppy none the less i.e poor plaster work, crooked corners in the interior walls, firewall not installed according to manufacturers specs, concrete feature pillars at the front of the house we visibly crooked.
If you choose to go with Ausbuild, I highly recommend paying an independent building inspector to check every stage of the build (i didn't), and be tough on the quality and hold progress payments where necessary, else I think you will likely be disappointed with their quality of work.
I personally will never build with them again. I don't view choosing them as a completely bad experience, as it taught me some very valuable lessons in home building that I will apply to the next chance I get to build.