The Tomix model 4034 Condominium and the Kato 23-485 Office building are a couple of staples of Japanese model buildings and are very adaptable. Also seen here is the Tomix 4038 Pachinko Hall.
These buildings have been attached to the modules for now in their stock condition. They come with quite a few detail parts and stickers. The way I attach them, they can be quickly removed for painting and detailing.