use google_project_iam_member as setting roles for grouped members

main.tf

locals {
  role_map_list = flatten([
    for role in var.roles : [
      for member in var.members : {
        role : role,
        member : member
      }
    ]
  ])
}

resource "google_project_iam_member" "iam_member_for_each" {
  for_each = {
    for role_map in local.role_map_list : "${role_map.role}/${role_map.member}" => {
      role   = role_map.role,
      member = role_map.member,
    }
  }
  role   = each.value.role
  member = each.value.member
}

variables.tf

variable members {
  type = set(string)
}

variable roles {
  type = set(string)
}