My parish council undertook a renovation of a sports pavilion to the tune of £250k with a £100k grant from the Football Foundation. The first thing I insisted on (as a Clerk) was that the council appoint a project manager with experience in building renovation and that I was totally unqualified to lead on this project. They fortunately agreed (although some thought it would be a simple job) and we then left the project manager to oversee the works. He was also involved in the tendering process for the builders. So the only approval the PC had to make was for the total cost of the project (apart from the appointment of the PM) as it was a fixed cost job.
There clearly was a fee involved and as a rule it is a % of the cost of the works. That said, it was worth every penny as the PM know exactly what had to be done, when and in what order. Getting happy amateurs to undertake this project would have, in the end cost more money.