I usually work with someone like Jack.......... unless it's a smaller job where I would take care of it myself.
Survey first, then Design, layout etc. Only call in a Structural Engineer to calculate loadings and steelwork that may be needed.
As has been said, a good JackTheHat would know decent builders....... ones who are most suited to the job in hand.
I'm really only repeating what the others have said. Your architect/Designer would apply for PP and organise Building Regulations, and collect probably three quotes.
One of the regulars on this site has hired a Project Manager. OK if you're building the Channel Tunnel, but an expensive and unnecessary expense for you.
There is only one word to remember on a project like this ........ Communication !!!
Architect, Builder, and client MUST all communicate and liase, to make the process enjoyable. Yes, it really can be enjoyable.
I always joke that the secret of good building is 1% skill & knowledge....... and 99% Attitude!