How does a real property appraiser adjust for land to building ratio?

Depends on the kind of property but generally the ratio is not particularly relevant -- it's whether there are comparable properties or not. Unless there is too much building and it violates local building laws. Then the appraiser might report a non-conforming use because at some point in the future the amount of building in excess of the laws could be ordered removed!! As another example of a twist, if the property is let's say a movie theater and local laws require X number of parking spaces of a minimum length and width and there are less than that number, again it could violate local laws as to parking ratios and if there isn't enough land to add more spaces the owner might be required to build and expensive parking structure, and the cost of compliance could affect value. Alternatively let's say it's a city lot with a 1-story building on it and all around are 10-story buildings, but this lot is too small and you could only build 8 stories on top. Then land might be valued less. If you want to be more specific, it may help us answer you.