Not really a master though, most of my altered melees are improvised noob GUI if you could observe the triggering on Faction Wars, but still doing my best to innovate stuffs.
Well, I could list down a few notes though, one of the most important thing in making your own melee map is to create an interesting balanced set of units, rather overflowing different units with the same functions, take Faction Wars again as an example, the Puma and Badger had too much comparison, the there's hardly a difference between two scouts, as a result, I'd be scrapping them out for EchoStorm. Also, try scrapping out some of WC 3's element, the lumber was a great example, so as the food and so on. And lastly, introduced them to the new stuffs, like a different kind of resource system. For EchoStorm, I have the specializations and EchoShard scavenging.
New skins, UIs, and music are always welcome on making RTS. ^ ^