I prefer Iridium but I've heard good things about this project.

1 - Download source:

git clone https://github.com/Eloston/ungoogled-chromium

2 - Read the instructions for building to debian based distros here

3 - Install some extra packages not listed in the tutorial above:
Note: Ascii has debhelper version 10.something installed so I had to choose a higher version for install. It is available in  devuan's backports repo

sudo apt-get install dh-autoreconf=17~bpo9+1

sudo apt-get install debhelper=11.2.1~bpo9+1

4 - Have all these packages installed for the build process:

sudo apt-get install packaging-dev python3 ninja-build clang-6.0 lld-6.0 llvm-6.0-dev python-jinja2 yasm xvfb gperf valgrind libglew-dev libgl1-mesa-dev libglu1-mesa-dev libegl1-mesa-dev libgles2-mesa-dev mesa-common-dev libre2-dev libgbm-dev libpng-dev libxss-dev libvpx-dev libpci-dev libcap-dev libicu-dev libkrb5-dev libexif-dev libflac-dev libudev-dev libopus-dev libwebp-dev libxtst-dev libsrtp-dev libjpeg-dev libxml2-dev libgtk-3-dev libxslt1-dev liblcms2-dev libpulse-dev libpam0g-dev libsnappy-dev libavutil-dev libavcodec-dev libavformat-dev libasound2-dev libjsoncpp-dev libspeechd-dev libminizip-dev libhunspell-dev libusb-1.0-0-dev libopenjp2-7-dev libmodpbase64-dev libnss3-dev   libnspr4-dev libcups2-dev libevent-dev  libjs-excanvas libjs-jquery-flot libgcrypt20-dev libva-dev

5 - Setup build space:

mkdir -p buildspace/downloads # Alternatively, buildspace/ can be a symbolic link
./buildkit-launcher.py genbun debian_stretch
./buildkit-launcher.py getsrc
./buildkit-launcher.py subdom
./buildkit-launcher.py genpkg debian --flavor stretch

6 - Finally, build it:

dpkg-buildpackage -b -uc

After building, the debs will appear under buildspace/

7 - Install it, in my case, I build it from master which is today at version 66.0.3359.139-1:

sudo dpkg -i buildspace/ungoogled-chromium-common_66.0.3359.139-1~stretch_amd64.deb
sudo dpkg -i buildspace/ungoogled-chromium_66.0.3359.139-1~stretch_amd64.deb

At this point, you are good to go, buy maybe you want to install some plugins:

8 - Installing addons/extensions
You may notice that it will not be possible to install plugins directly from Chrome webstore but you can follow this simple to do so:

8.1 - Make a directory to keep the extensions sources, chose whatever name you want for the dir:

mkdir ~/.ungoogled-chromium-extensions

8.2 - Download the crx extension file:
For this example, let's assume I'm installing AdBlock, so I'll get its webstore link and give it to http://crxextractor.com/.

8.3 - Convert the crx to zip file:
In the same site crxextractor, upload the crx in the option to convert it now to zip. It would be faster if they just let us convert the webstore link directly to zip but the site doesn't offer this service.

8.4 - Extract the zip content into the new created ~/.ungoogled-chromium-extensions dir

8.5 Install the extension from source into the browser:
> Go to chrome://extensions/
> Enable developer mode
> Click "Load unpacked"
> Choose the root directory of the extracted extension sources
> Have fun

Any suggestions to facilitate this process is welcome