I have recently had a promotion to site manager after years of working on sites as an engineer. My work as an engineer has kept me 60% on the road solo and 40% with other engineers in the team. I have taken numerous courses in my own time to compliment my position and this has been recognised and acted on by a promotion to site manager. This is where my problem starts. I feel lost in the new position. I am trying to find my focus and work out where I fit and where I can make a difference but the position didn't exist previously. The days I have out of the office are great for me, my comfort zone, but this cannot continue if I want to be a good manager. Any advice for new managers would be greatly appreciated and is this a natural reaction or am I an isolated case.
You are in your comfort zone on the road because being on the road is familiar to you. Since the position of site manager is brand new to you and your company, there is a lot of structure and a lot of details to be filled in that you have to put into the position, before the position conceptually makes sense to you, your company and anyone else. Yep, you have to create your own job.
As for your doubts that you are a good fit for the position, I'll reverse the question: how can you be a bad fit for a position that you get to shape your way? In order for you to be a bad fit for a position that you get to design, you have to be going out of your way to screw yourself.
I suggest that you go on Linkedin and on Google to look up the profiles and duties of site managers. There must be some site managers who are blogging, too. You can compile your findings into a general job description. You'll have to fill in the blanks, e.g. the details, as you gain more experience in the role.