Hi,
The Ruby API <https://developers.google.com/sketchup/docs/ourdoc/sketchup>is a module/classes that "communicate" with the closed-source C++ code
inside the program SketchUp. The methods of the API itself don't create or
modify a model, they just call the corresponding methods inside SketchUp.
That means the Ruby API works only for SketchUp plugins that run on Windows
or OS X. The Ruby API does not work stand-alone with a standard Ruby
installation.

The C++ SDK <https://developers.google.com/sketchup/docs/downloadsdksubmit>is for reading and writing SketchUp files (understanding the skp file
format). You would not only use it to write SketchUp *plugins *in C++ code,
but also (outside of SketchUp) to add to *another software* the ability to
read or convert skp files. I don't know enough about the SDK, but maybe it
also has methods to modify geometry.
So from the data in your database, you would calculate the needed geometry
(either with normal mathematical formulars, or maybe the SDK has more
convenient methods) and then write that geometry into a new skp file using
the SDK.