OK, so first off all you have to open or create your own map. I will use my "Desert storm map".
The second thing you need to do is make the skirmish arena. This is basically the whole map. So you have to select the polygon tool (marked with red).
And now click on the four corners of the map like this:
When you will click on all the four corners In the right side panel type "Skirmish Arena" (marked with red). Now you need to make the point where the players will spawn. So select the waypoint tool (marked with red).
Then in the right side panel select "Player_1_Start" for 1st player "Player_2_Start" for the second player and so on and click on the place where you want the first player spawn.
Now to let the Ai build it needs some build space. So now you have to select the polygon tool and make the place around the "player_1_start point", like this:
Next you need to make the place where the AI will build its defenses. it has to be named "OuterPerimeter1" and it has to surround the InnerPerimeter for 1st player and so on.
//OuterPerimeter is made like the InnerPerimeter. Now the AI is almost done. There's just 3 things left the CombatZone, the teams and the attack waypoints.
So first of all the combatzone. Its the place surrounding the whole battlefield except the player and AI bases. So it basicly covers all the map except for the player bases. To make the "CombatZone" You need to select the "polygon tool" and mark everything thats on the map and around the bases. So mark everything around the bases and when you do so On the right side panel in the selection place type in "CombatZone". Like this:
//The yellow line is the "CombatZone".
When you completed the CombatZone you need to add the "attack waypoints" that the AI will fallow when attacking. So basicly what you have to do is click on the "waypoint tool" and then on the CombatZone and drag to the InnerPerimeter of the players base and label it "Center1" if its 1st player base and so on. Like this:
//The arrow indicates the direction.
Then make another one like the first one and label it "Flank1" and another one and label it "BackDoor1". //Make them in different places to one base that wya the harder the AI the more directions it will use to attack. And now the last part make the AI. To do so just click EDIT > Edit player list > Add Skirmish players.
That is it finished, now your AI should work try it and if you have any problems download my mappack in my user > addons and check the waypoints or just post a comment.