Building a detached ADU isn’t necessarily different than building a house. accessorydwellings.org
And actually, quite important.
It's a new site and I wish it well. I'll be reading.
Many years ago I approached an editor at Sunset and suggested some article about ADUs. She snorted (though kindly) and told me that Sunset management would never allow anything but single-family houses. I suspect that times have changed big time.