Sap S4 Hana security implementation approach

Hello All,

I am working in a new green field implementation project , where I am handling role of security implementation for S4 hana. Everything is good with the security strategy of which roles to be used and naming convention ..etc ?

But when it comes to realise phase , I am not sure how to start with Roles discussions with the business teams .. For example , we have catalogs , groups , and also Business roles and Authorization data to be maintained, what will be the trigger point to initiate discussions with business teams ??

If any one of you can help me what is the 1 level of discussion we need to do initiate for security roles implementation ?