It seems like the build.sh script it is specifically designed for Debian-based distros. Also, there are some permission errors that come up. Thus, there are some minor changes that one needs to take into consideration while running this library on Arch-based distros.

1. On line 17 of build.sh change swig3.0 to swig-3. Also, if you don't already have swig3 installed, remember to install it from the archive, as you specifically need this version. sudo pacman -U https://archive.archlinux.org/packages/s/swig3/swig3-3.0.12-3-x86_64.pkg.tar.xz should take care of that.
2. Personally, I solved the permission errors that come up while running python setup.py install, because running sudo python setup.py install didn't work for me, by using pyenv. Particularly, I am using python 3.6.0, but perhaps there is another version that works. (Just as a reminder, remember to install the dependencies for PyNEC, if you weren't already using pyenv)

I believe those are some of the major "patches" that I implemented, but feel free to add something else if it's needed for other systems.