How do I combine faces of cubes?

I'm trying to combine the faces of many 1x1 unit cubes into a bigger cube, so that it renders much faster than they would seperately but so that when one cube is removed it will still render the 'chunk' missing from the bigger cube.

I am also hoping that this would help to render the semi-transparent cubes together rather than individually where you can still see the other faces of the other cubes still being rendered, not the ideal effect for a large semi-transparent block made from many smaller prefabs.

Check out the procedural mesh examples on the Unity site, and perhaps also search Unity Answers and the forums for 'minecraft' (as this sounds like essentially the same problem, and the topic has been discussed quite a bit here and on the forums in the past).