Hi,
$ yum -v grouplist | grep -i development
Development Libraries (development-libs)
Development Tools (development-tools)
GNOME Software Development (gnome-software-development)
Java Development (java-development)
KDE Software Development (kde-software-development)
Legacy Software Development (legacy-software-development)
Perl Development (perl)
Web Development (web-development)
X Software Development (x-software-development)
XFCE Software Development (xfce-software-development)
So what you really need is @development-tools. For custom repository, let me point to an example
http://omega.dgplug.org/11/Live/i686...1-i686-Live.ks
You can dump the packages into a folder, run createrepo -d on them and point to them using file:////
Rahul
http://fedoraproject.org/wiki/RahulSundaram