Gentoo provides an automated set of scripts (ebuilds) for compiling KDE from source. The base KDE packages can be found in the "kde-base" directory of portage (/usr/portage/kde-base/).

To get the latest set of builds, perform this step:

emerge sync

You can then emerge the latest set of builds. An example:

emerge kde-base/arts
emerge kde-base/kdelibs
emerge kde-base/kdebase

Or, to install almost all KDE packages:

emerge kde-base/kde