Either of two formats seem to work best for our clients.
1 Firm bid contract or
2 Construction Management contract

Both are very different.

Firm bid is a locked-in format that a project, upon a signed contract , is handed over to a contractor and in turn, fulfilled for a specific sum. The price is specific to the items allowed for. Changes in this case become change orders

Construction Management is a partnership between a client and a contractor where the Manager oversees the project for the client for a fee (usually a percentage of job cost). An estimated budget is used as a template to create the desired home. The client has the freedom to make changes and the Project Manager works with the client analyzing any extra costs involved.