I work for a builder in SA. I would say in my experience dealing with people and having built myself, everyone thinks of going to the big project home builders because they seem to be cheaper initially, but they dont include HEAPS of stuff. I would work out exactly what you expect from the build and then shop around a few custom builders and maybe one big project builder. You just want to check they are all including for the same things because there can be big price differences in things that you may think are only small.