When installed with pip you don't use buildout. There is no buildout file needed.
Addons are also installed with pip, here is an example with plone.reload==3.0.2:
${PLONE_HOME}/bin/pip install plone.reload==3.0.2
Addons that are "editable" and in your local path (i.e. setuptools "develop mode") are also installed with pip but in "editable mode" with the option -e:
# create src directory for you addons
mkdir ${PLONE_HOME}/src
# create your addon directory struture and files in ${PLONE_HOME}/src
...
# install your addon with pip in editable mode (i.e. setuptools "develop mode")
${PLONE_HOME}/bin/pip install -e ${PLONE_HOME}/src/myaddon.name