If you want only the building footprints in a format that's easy to use, I created this workflow a couple years ago. It's for Clatsop County. Just change it for your area.
https://github.com/bwilsoncc/clatsop_buildings
Source for Australia is here https://github.com/microsoft/AustraliaBuildingFootprints
I evaluated the Microsoft building footprints in my area, decided they were good enough for now in county projects but decided to use more care when putting them into OpenStreetMap, there are lots of errors here. They are not good enough in my opinion for OSM but it depends on what you are doing. In my area they were... so so.
What does Microsoft say?
"Should we import the data into OpenStreetMap?
Maybe. Never overwrite the hard work of other contributors or blindly import data into OSM without first checking the local quality"
But HEY, they are not importing the so-so data into OSM, they are blindly overlaying my hard work with it instead.