Everything you do in real estate first has to take in location. This is very important !
You never want to "over build" for the neighborhood or location.
If there are similar homes around you with those additions and they are in good condition,
it could give you a decent return.
I do have a chart called Remodeling Cost vs. Value. You would be surprised at this information.
Glad to send it to you.
I would be happy to come by and take a look. I could do a CMA with and without the garage. Send me an email if you want me to take a look.