@Scott Mac, Thanks for your comment. Sorry for the delay in answering, got busy. How to keep costs down? Question everything. Costs come in many guises. Time costs, material costs, regulatory costs and mistake costs. Think of each one as something you need to pay attention to.
Time costs: Every minute costs you money. Scheduling your subcontractors is a tricky business. Say you have 7 different subcontractors that need to be on site one after the other. They all have their own schedules and you are only one of them. This is, again, another relationship building exercise. Don't expect them to show up on X day just because they said they would. Keep in touch with them as their turn is coming up, like two weeks ahead to confirm. You will be on the phone a lot. And always be nice.
Material costs: Most of your materials will be commodities and no one can do too much about that. However, find suppliers that will go beyond the sale and take care of you. That is valuable. This can only come with experience. But when you are short one beam hanger that is hard to find and they bring one out from 20 miles away for free so your framer can keep working, that's valuable.
Mistake costs: Your suppliers, your subcontractors and you will make mistakes. Your suppliers should own up and make good. Your subcontractors are going to be a mixed bag. If you really understand what they are doing you can spot their mistakes. This is about keeping your eyes open and seeing to it that they fix or repair their own mistakes. Some of these can be very expensive.