You MAY be able to get away with hiring yourself a New Home, ASHI-Approved Home Inspector. (I'm not one of them, nor am I affiliated w/ASHI, nor am I compensated by them in ANY way. Visit their WEB site to see why they come highly recommended IMO.)
A New Home Inspector will inspect your construction at a number of critical 'intervals'. Foundation, Framing, Plumbing & Electrical, Roofing & Siding, and Finishing, to name a few. They will most likely inspect a variety of 'things' at different junctures. This way, you'll have 1) someone who knows what to look for, and 2) someone working in YOUR best interest. I agree w/jb in that this is a big issue. You may want to consider either hiring an architect to review what plans you have (or make plans), or a General Contractor to 'oversee' your project. These are the types of people that you 'communicate' your concerns to, PERFERABLY, before a particular job or aspect of a job begins. Talk to all 3 types of Professional Helpers for how they'd go about looking after YOUR interests. Don't even ask them about cost until you FINISH hearing what they do for you. Price should be the last factor because the FIRST factor is to see if they'll do what you want them to do, and/or more. As with all 'items' for the person you eventually hire, you can negotiate price. I'd just refrain from asking about it until you're satified with what they're gonna do, or not do, for you.
My best to ya and hope this helps.
PS: It is also a 'good thing' to retain a Real Estate Attorney to look over your paperwork BEFORE you sign. Preferably someone that's familiar with Real Estate Contract Law. An architect or a General Contractor or even a Home Inspector should be able to get you some references. Some of these folks even use them themselves to protect THEIR interest(s) ...