Before you start you have to have a solid local data source. Users demand accurate data including all the fields normally important in any directory including base data, extended data such as hours, types of payments, specialties, accurate categorization, and more. You will need to develop processes to clean and normalize the data, and maintain the add/deletes/updates. You will need update process allowing businesses to self-fulfill, but also need verification processes to limit changes to data by the owner of that data. You may be able to use a white label version from a national provider, yet they often require minimum revenues and customization fees. Directory is always about accuracy.