Hey, i think you can make an offense map like DOTA, but with more innovation. i suggest that map has many heroes and many custom spells. I will help you for this, i have many idea to make simple and exciting spells. an then the map has mercenaries and secret path to do ambush, so that the player can use his mercenaries to create an ambush or just to force forward. Also modify gameplay constant for hero's attributes so that it will has lower hitpoints and high attack damage. Those makes many killing events on the game. For item you can make an item that can be upgraded repeatedly, like:
Boots of Speed
Boots of Speed #2
Boots of Speed #3
Boots of Speed #4
Boots of Flash
It can have 5 level or maybe 10 level, so that a player can focus on one item and make it greatest.
For the terrain you can make terrain that has secret power up like double damage, rage, and so on, but also has secret trap on some point on secret path that has been through evenly. The trap can be spiked trap, frost trap, poison trap, or anything.
Has many extra mode (-allrandom, -allpick, and so on) and has bounty on each player.
the bounty can raise if the player kills another hero, gains a level, acquire an item, or maybe amount of unit killed (it is up to you). The bounty also can decrease if the player killed. Those will makes the great player to become worthy and were hunted and the stupid player will become worthless.
I can help you for making spells and items. And if anyone has a home page, we can put the map on it, or maybe make new home page.
Wow, those are my idea. if you wanna create it, please ask me a favor, i will help you.