Are you going to develop a CMS as a module for DNN, or as a stand alone CMS?  Naturally it would be silly to ask how to create something that doesn't use DNN in a DNN forum, you would want to use the forums at www.asp.net.  If as a module, you'll first have to define your CMS goals, and how it will interface to DNN as a module.  You should be able to put your recent education to work in creating the project specs and scope, defining project milestones and accomplishing those within your time frame.  Along with testing, deployment, documentation and deliverables.

Jeff