Concrete vs Stick build

[Squirl]

Check with your zoning and your building departments.  The upstairs of the garage has a bathroom and bedroom in the plans.  They will probably treat it as an apartment.  You will have to go through all the same code and building provisions for a house.  Also, IIRC my zoning (a few counties over) states only one habitable building per property.  I believe you would have to be zoned for multiple unit residential to be approved for more than one habitable building per property.  I'm just giving a heads up.  I would hate you to build the garage, then apply for your house permit and be denied.