Hi
You would need an accountant to create the COA required by the business, then a NAV developer to go through the requirements of the NAV system to map the various required posting group accounts to the COA.
A lot of this will also depend on what areas of the system the client will be using, so Inventory, manufacturing, service...etc
If you have a more specific question put it up and i will try to help
Cheers
Nev