Best way to lean about Payroll Schema Configuration is to take SAP's HR400 (Payroll Configuration) course, followed up by the Country Specific Payroll Course (in the HR4xx series).
SAP also offers online documentation, such as Configuration - Payroll United States (PY-US) - SAP Library , all you have to do is do a little search online.
You can also get documentation on SAP PRESS Bookstore, in the Wikis from this site, and elsewhere on the web.
You will also need to gather your client's requirements, copy the standart Payroll Schema for your Country Code(s), and modify the copy (or copies) to meet these requirements.