I think Bob also raised a few good points.
Ensure a construction program is included into the contract, along with a progress payment schedule (naturally should be anyway).
Regarding progress payment schedules, be careful the builder doesn't increase the earlier progress payments by too much and decrease the later progress payments. They do this to help with cash flow and decrease the chance of you ripping them off towards the end of the project, but it'll cost you more interest.
The 3 most important aspects of the contract are quality, time and cost.
Cost= Schedule with breakdown of costs, progress payments (how much/when/percentage or stage completed), and total sum. The toughest part about cost is when builders aren't clear about what is included and excluded, and what they appoint provisional sums to. So this'll take some of your time to compare apples with apples (other quotes). Also, ensure an amount (%) is retained (retention) until after defects liability period. This'll ensure the builder will return to fix defects, and if not you can pay someone else using the retained funds. If I were you, I'd make it VERY clear to the builder prior to signing the contract that ABSOLUTELY NO, NONE, ZILCH, NADA variations will be accepted, but make sure you say this after they've submitted a tender and when there hanging for you to sign and return the contract. lol
Time= A detailed construction program, completion date, liquidated damages clauses if time has been exceeded. On the contrary to liquidated damages, a bonus clause for the builder is also beneficial for both parties. If the builder completes a month early, it'll save you interest and you could pass on some of those savings to the builder as an incentive.
Quality= The quality aspect can take some time to prepare, but it's where you'll ensure the builder delivers your expectations. Design documentation, schedules, written statements (principal project requirements) outlining fitments and finishes (with make, model, sizes, etc), and any other info you can think of. Above all, make sure nothing is verbal and everything is written from the onset.
From my experience, the client side PMs I've met and worked with have been guys who don't like to dirty their RM Williams boots. They will be able to help contractually, but when it comes to quality inspections, I don't think they'd have the slightest clue. If you were to go the client side PM route, you may have to employ an engineer for site inspections.
I'm not sure if building consultants offer this type of service, but perhaps you could look into them. Building consultants from my perspective have had a more hands on and problem solving upbringing, so they may be able to provide more insight through the entire project, from concept to completion. The ones I've met have come from trade backgrounds, completed projects for themselves and then become consultants due to the pool of knowledge gained from all the damn problem solving. So I think they may be able to help you with design, contract, and inspections.
Depending on which you wish to swing, you can also appoint the PM or the consultant as the superintendent of the contract, which'll give them special powers and enable them to give instructions to the builder.
Otherwise, you could take a risk, same some dosh and find yourself a good, honest builder. They're out there, you just gotta find one. I guess this is where you're ability to judge characters comes in. I've been heavily contemplating on starting my own gig and I think it's about bloody time too!
Good luck $horty.