I have some experience in creating maps for Heroes 3 (I created two maps: M and XL
M - the first test map, 4 factions, you could say it's a standard map
XL - I think it turned out well, I played it myself =) It was called "Good and Evil," 3 vs. 3... unfortunately, I don't have the maps anymore =(
I created few maps because I didn't have much time, and I didn't really feel like it...
Creating and playing alone isn't interesting either...
In Heroes 4, I started creating a map, but I didn't finish it... I have little experience, but that's not a hindrance...
There's no editor for Heroes 5 =(((

I can also test maps and try to come up with a plot =)