Building rpms with make

I'm trying to automate building a set of RPMs for a yum repository and
am kicking around the idea of using 'make'.

I'm having trouble figuring out the generic RPM build rule.  I'm
guessing that having the version and release numbers, and the
architecture encoded in the RPM name is going to complicate building
such a rule.  Presumably it's not as simple as:

	%.rpm : %.spec %.tar
		rpmbuild -ba $*

Could someone point me at a makefile that does this kind of repo 
management (i.e. builds dozens of RPMs from dozens of spec files)?

Regards,

	Richard Siddall