There are several common approaches to project delivery, however, we have outline the two most common construction methods below.
First the contractor is usually interviewed and selected before or during the design process. This allows the owner to select a contractor based on compatibility, experience and qualifications in lieu of simply a construction bid. Another benefit is the ability to streamline the process is improved. This does not mean the project is not bid out because the contractor still bids the project to his sub-contractors, however, he has significant leverage with them knowing he already has the project under contract. This leverage puts him at an advantage with his sub-contractors during negotiations. The leverage can be realized in many forms. It can be the obvious lower cost, improved scheduling and/or adding scope to the project while minimizing the cost impact, schedule, etc. This typically means the contractor can either bid the project to their sub-contractors in an open book fashion so all of the numbers are transparent and the contractor then adds his markup to the total cost, or the contract for the construction is a negotiated fixed fee with the contractor at the onset of the project.
Another benefit is that the engineering can also often be simplified for these less sophisticated projects and submitted for permit after the architectural has been applied for. This is referred to as a deferred submittal. Mechanical, electrical, plumbing, fire protection, truss engineering, are the most common deferred submittals and they can usually be submitted shortly after the architectural or building permit has been issued. Not all municipalities or project types allow deferred submittals, but this approach can often shave weeks off of the schedule. Framing layout, trenching for plumbing or electric, demolition, etc. can all begin while the deferred submittals are being reviewed for permitting.
If the contractor is under contract during the design process they can often make recommendations for efficiencies that can be used to save time, cost, material, etc. They can also provide real world, project specific cost estimates during the design process. This feedback can allow design decisions that may need to be driven based on a projects budget earlier in the design process resulting in the most efficient design solution that may be constrained by a specific budget.