A key decision that any prospective self-builder will need to make is that of whether or not to employ an architect. I'm biased on this issue and would always recommend that an architect be appointed.
There are plenty of "plan drawers" and "architectural designers" out there, and they WILL generally be cheaper than architects, but the saving could turn out be a major cost in the long run.
Architects are professionally trained and registered and carry proper Professional Indemnity insurance. Find one that you click with and they will be a great asset to your project and you'll have the reassurance of reliability and quality.
Of course, not all architects are good, and not all plan drawers are bad but do you want to take the chance?