Save both the building block and the macro in the same template. You can decide where to save both of these as you create them or move them later. Where can Building Blocks be stored? Organizing your macros by Beth Melton, Word MVP

In that situation, the location of your building block for your code will be in the template: ThisDocument always refers to the name of the document that holds the macro. Fullname gives both the name and path automatically.

If the building block is used in multiple templates, it should be in a loaded global template and have a unique name. In that case, look at the macro for situation 3 on my linked page.