The installation from source is described with a lot of detail at the openbabel website, however to give a quick reference here are a few cmake parameters that may be of use when building the package:
-DEIGEN2_INCLUDE_DIR=<path to eigen2 folder>
Beware: cmake can get confused on your system thus it you should not make the install path the same as the build path, i.e. if you call cmake from within a folder called 'build', don't use the path to this folder for DCMAKE_INSTALL_PREFIX!
Also it may be that cmake does not recognize the correct python compiler. Here it is then useful to also add the following parameters to the cmake command:
-DPYTHON_EXECUTABLE=<path to python executable, e.g. /usr/opt/python-x.y.z/bin/python>
-DPYTHON_LIBRARY=<path to python lib, e.g. python-x.y.z/lib>
-DPYTHON_INCLUDE_DIR=<path to include folder of python, e.g. python-x.y.z/include>
It is noteworthy that for me compiling openbabel with eigen3 did not work out so I had to downgrade to eigen2, then everything worked fine.
The general install procedure is then in the downloaded and unpacked openbabel directory
cmake .. -DCMAKE_INSTALL_PREFIX=/... -D<other parameters>
make -j8 (-j parameter is used for parallelization of make process)
(sudo) make install
More information about how to use openbabel can be found in the documentation.