Start with what you can access
Describe the rooms and appliances you want to back up. Note where the meter and distribution board are located and mention any areas you cannot access. Use photos from accessible positions and let the installer inspect wiring and mounting conditions during the visit.
Agree on changes with the property owner
Ask the owner about roof access, permanent mounting and cable routes before the visit. Confirm who needs to approve any work and what happens when you move out. Share those constraints with the installer so the proposal reflects what can actually be installed.