The typical way to build buildings is through a design-bid-build approach. The way this works is that you first design stuff and create drawings. You then ask people to price the stuff that you have drawn. And then you proceed to build what is on the drawings and what has been priced.
There are a number of possible risks with this approach. For one, the design/drawing phase is sometimes/often done in isolation without a lot of feedback from the contractor and/or subcontractors. So you might be designing and drawing things that aren't all that feasible or constructible. Pre-construction involvement helps address this.
Another risk is that you're buying what is on the drawings. So if the drawings suck or aren't properly coordinated, then you are likely opening yourself up to a barrage of change orders and lots of additional costs.
In theory, it all sounds fine. Here are my drawings and specifications. Give me a price. And then let's build. But as many or most of you will know, it's generally never that simple or easy. Though it will, of course, depend on the type and complexity of the project.
Another consideration is the kind of contract you enter with your constructor. Is it a cost-plus contract, where the constructor simply charges a percentage on top of whatever the costs end up being, or is it some kind of lump sum or guaranteed maximum price (GMP) contract?
While I was in architecture school I decided to take a class on construction delivery methods. The instructor was, in my mind, your quintessential construction person. He was built like a brick shithouse and he never minced words. He also had a voice that sounded like a subwoofer.