I know Tower Defense maps are abundant now, but I created this one for a special purpose: To show how to spawn units over time to form a line, rather than just a certain amount of units in one go, which is what I've noticed nearly every map so far has been doing. This is slightly more complicated, but by looking at my triggers you'll see it's fairly easy to do.
Also check out http://www.youtube.com/watch?v=SBQjnT_96hQ&playnext_from=TL&videos=Uj409AyEEx0
It's the tutorial I roughly followed to get the basis of my map, and then edited significantly to create the conga-line style of defense instead of the 'all units in a wave at once' style that the tutorial teaches.
Beyond that, 8 rounds, pretty basic.