First of all three team AOS' is not a new thing. I've made a 3vs3vs3 aos which i never updated after patch 24b, so you might want to think about the following:
3 teams generally mean a larger map. This resault in various things:
>Larger maps tend to lag more due to larger amount of doodads etc.
>Larger maps require more terraining work
>Larger maps mean less action
A huge problem with the triangle is you'll have a triangle shaped map within square boundaries. This will cause a large amount of the map to be *wasted*
Another problem with three team AOS' is that two teams tend to pick on another team.
One of the worst things about an AOS is your map will probably never become popular. People will always compare your AOS' to DOTA or MOBA games (League of Legends, Heroes of Newerth, Demigods). The genre has been squeezed to its limits in attempt to bring something new to gaming. Don't get me wrong here, AOS' are great, fun to make and a awesome genre, you'll just have to implement really innovative ideas for your map to be successful.
Things you can implement:
A HUGE problem with warcraft's hero system is...Int heroes tend to SUCK once ability scores tend to get too high. Agility heroes having increased attack speed and damage reduction tend to obliterate other heroes and strenght heroes are somewhere in between.
Set all ability cooldowns to 0 secs. Create 1 dummy unit for each activated ability. Now let ability 1 require unit 1 as a tech requirement. and ability 2 require unit 2 as a tech requirement etc....Whenever you cast a spell the owner of the corresponding unit gets set to Neutral Passive and reset to the original owner after a few seconds. This allows you to mimic the cooldown system, BUT you'll be able to reduce/increase ability cooldowns. This way you can make intelligence reduce ability cooldowns!
Code all your abilities to deal damage based of attributes
Really brute force. Implement League of Legend's system. Remove all attributes and implement a unit properties system. Then cause a hero to gain life, damage, mana, armor, life regeneration etc. when the hero gaints a level. This allows you to screw the primary attribute system which as a bonus allows you to build almost any build with any hero since you no longer have to buy agility for "agility" heroes or strenght for a strenght hero.
Concerning gameplay: Dota's gameplay is old fasioned. You'll need to add some nice additions. Some things that have been done before that you might want to implement:
Neutral monsters that grant buffs if killed (League of Legends)
Capturable areas that grant bonuses (Demigods and some AOS maps)
Remove denying, which cause early game to be alot more aggresive and contain less of the *sucky* defensive play you find in Dota. (League of Legends)
Add moral...each hero and creepkill slowly improve your creeps (LOTS of AOS maps)
Add upgrades for your creeps (Demigods and some AOS maps)
Allow you to customize your items by adding bonusses of your choosing (very few aos maps)
Remove towers and replace them with towns. Towns change their ownership if destroyed.
Cause neutrals to drop charged items like potions etc.
Where you normally have a tower, replace it with 4+ towers. Players can build towers at the cost of resources ( some aoses)
Allow players to add additional units to waves of creeps
Allow players to buy tempory powerups for their team which turn the tide of battle (some aoses)
