I would like to create a Build Definition inside TFS 2012 Express which will simply copy all files within my project source tree to another folder on my drive. Just to underline
I actually put something together for TFS2010 and 2013 (not 2012, unfortunately) a few weeks ago that does exactly that. Basically, anything in the workspace you define for your build just gets shoved over to the drop location.
Here's a link to the blog post where you can download them:
http://www.incyclesoftware.com/2014/06/deploying-uncompiled-resources-release-management/
For the record, I strongly recommend against using a build process template to deploy software. Don't try to overextend the build... its job is taking stuff from source control and compiling/packaging it for deployment. Use a real release management solution to actually handle deploying software.