Reinstall the kernel sources if you need to. Create the BUILD directory if you need to. Change to the ~/rpmbuild/kernel/ directory. Then use the rpmbuild prep stage to apply any patches.

rpm -ihv kernel-XXX.src.rpm
mkdir ~/rpmbuild/kernel/BUILD			
cd ~/rpmbuild/kernel/
rpmbuild -bp kernel-XXX.spec
		

You should now have a fully patched copy of the source in the BUILD directory. Take a look at contents of BUILD/kernel-XXX/linux-XXX/. For me they are:

.            .config.old  Documentation  ipc          mm              security
..           configs      drivers        kernel       net             sound
arch         COPYING      fs             lib          README          usr
.config      CREDITS      include        MAINTAINERS  REPORTING-BUGS
.config.cmd  crypto       init           Makefile     scripts