Note that you need to have a .config file that will be included in the build. It will also use the Version as specified in your Makefile. Then run

make rpm-pkg

Which will use the RPM build infra set up for your user to put the rpm in $HOME/rpmbuild/

Edit: Note that a bunch of dependencies are needed to get the Kernel to build. If you run the above command and it fails out with a message that you are missing a dependency, you can use this pair of commands to get the yum-build dep tool installed, and use that to install the dependencies as listed by the generated kernel.spec file.

wget https://src.fedoraproject.org/rpms/kernel/raw/rawhide/f/kernel.spec
yum install dnf-utils
yum-builddep ./kernel.spec