You will have separate contracts with the architect and the builder so they will do what you ask them to do. If you want them to collaborate with you in design and cost meetings and copy each other with what they send you they will do that.

However, the architect will be solely responsible for the design and construction documents and the builder will be solely responsible for the construction of the project.

If you ask the architect to be involved in the construction phase you should state what his/her role is in your contract with the builder. That role can be to observe the progress and general quality of the work and report to you or it can include the right to reject work that does not conform to the contract documents. The architect might review the contractor's invoices and advise you informally or the builder might be required to submit applications for payment to the architect for his signature before sending it to you.

So, how they interact depends on the kind of services you want. What you describe is unusual in home building but standard procedure for larger projects so it helps if the two parties are experienced in a wide range of project sizes, contracts and management techniques.

You have received good, professional advice.

Will you use an architect? What will be the scope of services: design, bidding assistance, construction contract administration and project close out, or what?

Will you use a single contractor to work with you and the architect, and thereafter build your house? How will you compensate the contractor for her/his time during design and prior to award of a construction contract? Or will you competively bid the project for awarding a construction contract?

How will you compensate each party for their respective services? And who is the decision-maker and has responsibility/liability for each respective phase of the work?

Have you thought this through?

You really need to give a lot of thought to what you want these two parties to do, how you want them to do it and how you want them to take responsibility. These are two different individuals, representing two seperate businesses where they make their livings. How they represent your best interests is the key question.

If you should decide to go to a single design-build firm for design and construction services, the challenges increase. For example, who represents your interests as the owner during bidding and construction? And how do you know what the costs really are for design and subsequently for construction?

There's a lot of due diligence needed here.

Good luck on your project.