Ubuntu does not support the LEMON package but "OpenROAD/src/TritonCTS/CMakeLists.txt" looks for LEMON during installation. I had to comment out "find_package(LEMON REQUIRED)" do get past the error in the CMakeLists file. Not sure if this is a correct fix.

The following two files have SWIG version hardcoded to 3.0 on the line "find_package(SWIG REQUIRED 3.0)"
OpenROAD/src/OpenDB/CMakeLists.txt
OpenROAD/src/OpenSTA/CMakeLists.txt
Using a different version of SWIG while installation throws an error.

Unable to locate tcl.h
OpenROAD/src/antennachecker/include/antennachecker/AntennaChecker.hh required editing the include to have tcl/tcl.h instead of "#include <tcl.h>"
OpenROAD/build/src/antennachecker/src/AntennaChecker_wrap.cc also required editing the include to have tcl/tcl.h instead of "#include <tcl/tcl.h>"

Filesystem error
OpenROAD/src/OpenPhySyn/src/FileUtils.cpp – needs to use experimental package for ubuntu on the following two lines
#include <experimental/filesystem>
namespace fs = std::experimental::filesystem;