This Dockerfile creates a docker that compiles the freeradius server v3.0.17 in a ubuntu xenial enviroment. It is basically a copy-paste of instructions available at this page.
This is not a container running freeradius.
docker pull epol/freeradius-ubuntu-compile
docker run --rm -v /some/dir:/packages epol/freeradius-ubuntu-compile
where /some/dir is the path where you want to find your compiled .deb packages.