What requirements/dependencies are needed for building Quassel?

The list is quite short: You'll need Qt 4.3 or higher with Sqlite3 support. To check for the Qt version you have installed, run "qmake -version" or (on some distributions) "qmake-qt4 -version".

More specifically, Quassel Client needs QtCore, QtGui, QtScript and QtNetwork. Quassel Core needs QtCore, QtScript, QtNetwork and QtSql (with sqlite3 support). The combined (monolithic) version needs a superset of these modules, of course :)