Hi Kenny-
I've written a few blogs about what an investor or first time buyer should look for in a property with ADU potential. The above comments have some great advice. I would add a few things. As you have probably figured out, each municipality has its own ordinance and guidelines, so make sure to do your research at each specific city. For properties in city of Los Angeles (with which I'm most familiar), for the most cost effective solution, look for a house with a permitted garage in the back. Make sure that the garage does NOT have power lines running over the top of it. The location of the existing garage is "grandfathered in", so there are no setback requirements to converting it to ADU.
The city of LA will make you run a new sewer line from the ADU to your front yard to connect to the main sewer. This can be a pretty large cost if 1) the ADU is very far from the street or 2) you have to cut into a concrete driveway to run the sewer (and then patch the concrete). Something to consider.
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