Professional advice during self-build
You are acting as your own general contractor, which is not unusual at all.  

The role you are describing sounds like a project manager.  I know of just one person that provides project management services as a third party for owners on small projects.  Project managers are generally employed by a general contractor working on larger projects.   

You basically need someone to provide part time, short term project management services.  If you can't find someone providing this service, you might find a project manager that is seeking full time employment that is willing to work part time short term;  you might find a working contractor, maybe a one man shop, that's temporarily unable to work due to injury.  You may find a retired contractor that's willing to provide this service.