It should work on most packages, however it won't work unless the source package contains
a makefile. Write one if you have to (it's not hard), a simple one will suffice
if it handles "install" it's fine. If the Makefile handles "DESTDIR" it will use
this to make the package (e.g. not actually installing the sources, you need
to install the package afterwards), if not, it will use installwatch (so you need
that - it comes with checkinstall).
In the latter case there is no option but to do a real install, but the package
means you can uninstall if needed.
Unlike checkinstall, mkpkg follows slackware standards exactly, however, at this
stage it ONLY creates slack-desc for you.
If you want other slack- files, cd to /mkpkg/$PACKAGE_NAME after building, modify
the package and rerun makepkg.

mkpkg is made up of one simple shell script (called mkpkg.sh) and a couple of
supporting binaries. When you are asked to type the description, don't worry
about formatting, just type it (but do follow the norm of putting an empty line
after the first line) - mkpkg will format your slack-desc file for you.

mkpkg logs your configure options, that way, if you build later (or build an update)
you get a reminder of the options you used before !