Here's my early version of Tower Defense map. At the moment you can build only few things like wall, 1 tower, base, probes. Your main builder is a unit that can build, gather resources and serve as base for your probes.
Cool thing is that you don't get minerals from killing mobs. You have to gather them on your own by building probes and/or gather yourself. You are walking base to where minerals can be gathered to. You can also build small bases on the map for shorted gathering way.
this video is from early version :)