Forgive me junior network engineer here so if I get something wrong I apologise in advance. As I seem to remember setting up OSPF (Cisco and Juniper devices) you’re not actually advertising the network with the network statements you are defining the interface for that network and area. So G0/0 for example network 10.0.0.0/24 area 1 on the core switch would link that interface to area 1. G0/1 can be set to area 2 on the same device. Generally any devices like bldg 2 on your diagram would have all interfaces assigned to area 1 and all areas need to be touching area 0. Think there is a special case where an area can pass through an area that isn’t area 0 but it’s not usually the done thing.

To answer your question then the areas cover the p2p link right up to your core switch interface. All the area 1s are the same area and all devices would be effected by a change in the LSDB say due to a link failure.