This is just my personal ~/.xmonad/ directory.
Well, if you are sure you want to...
These days I use this on Debian unstable, and build with Stack.
In theory all you need to do is to clone the xmonad and
xmonad-contrib repositories into the xmonad-git and
xmonad-contrib-git subdirectories. Then call stack install.
It'll put the standard xmonad binary in your stack local-bin-path,
but I hardly ever use that: instead, I use a .xsession file to
directly start the xmonad-$arch-$os binary. There's also a simple
build script to make XMonad's recompile action work as expected.
The custom code resides all in the zem subdirectory, formatted as a
Cabal package so that it can be built with Stack. Most of the bulk is
in the library (zem/src/), but there are also two executables to act
as the configured XMonad binaries for my desktop and laptop
setups. The only difference between them is the automatic Xrandr (and
in the future, DPI) switching, as the laptop gets used both with and
without external displays quite often.