im trying to build a skirmish map where 2 players attack one ai. ive built maps but experimenting something new. i want to have an ai with an already built base on the map at the start of game in skirmish but not having any success. the idea is 2 players have to jion forces to attack the heravely defended base of the ai controled player. i cant seem to get the ai to start. the other option is to be able to select which faction the ai can start with but also have the prebuilt base and therefore having 2 differant factions weapons. is this possible or am i wasting my time. ive currently have the prebuilt base as the boss charecter could this be a problem too. any help would be good. im not too good with scripting but i have built a number of maps successfully. hope you can help me with my problem.

GT1

I might be wrong but I don't think your idea is going to work. Any buildings placed on the map will be sold when turned over to an AI player. One way you could do this is to import the default AI scripts and spawn buildings for the third player. You would need to script it so the condition checks the players start position and whether they have built a supply center. If these conditions are met you can spawn your buildings. You would need to make a copy of these scripts in each AI folder. This does give you the option of making each base different depending on the faction starting in position three. As far as the AI using the boss war factory, I believe you would need to script some subroutines for them to build the unique units. I think this is all doable. So I would do the following to check this out.
*Import the AI scripts.
*Place waypoints where you want buildings placed.
*Starting with one AI, make a folder to contain these scripts and script the spawn script checking for start location and if a supply center has been built in the condition.

IF this checks out when testing, export this folder then import it into each of the AI folders. Modify the supply condition check for each faction. Then test again for all factions.

This will at least get you started. Let us know how it's coming.
I've attached the default scripts for Zero Hour.

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You might also want to check out the tutorial on making AOD map . That's kind of what you're wanting to make anyway.
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  AI_Scripts for Zero Hour.zip (225kb) downloaded 16 time(s).

Well you can spawn buildings on skirmish players, then they won't be sold. But if you want a human player to also be able to occupy the base, then it makes things difficult. But what may be best then is to make your map, then create a copy of it. With one, make it so that the base position is meant for a specific computer player. Then on the other map, to make it specifically for a human player.

Although having extra buildings may mess up a computer player.

You really don't need to make two copies of the map. Just use a marker unit (HumanPlaying) that is removed by the AI players. If the marker is there, buildings are spawned via civilian player and transferred to the human player. If marker is missing, activate spawn scripts in the AI folder for these buildings.