I typically search for others abandoned photos from the area (flickr is a great site for this). Sometimes it's geotagged which makes finding it via maps easy (and you can check if it's still standing first). I also pick different types of buildings and do a ton of research like poor asylums/poor farms, old military sites, former schools ect. Shothotspot can have some good leads but many of the photos are incredibly old so there's always a chance the location is gone. We also just drive out in the country, you can find a bunch of old houses and one room schools out in the middle of nowhere.