Making Formulas That Automatically Update When Adding Cells

I want to make an excel workbook for a client. What I want to do with it is make a set of instructions telling them to add or insert as many rows in specific categories I have made for them. These options differ depending on the different duties performed. There will be an associated number (value for that duty, ex. duty might be Janitor and the number would be like 5 dollars per hour, so on and so forth), I want to make it to where there is a code that notices more rows and adds more IF statements or whatever statements are needed to keep adding those extra options. These values are connected to a data validation list that drives the if statement.