Each skirmish player can garrison up to three buildings. You just name the buildings you want the skirmish players to garrison: PlayerX GarrisonY. (I believe this is case sensitive.) The "X" & "Y" are number verables. For the skirmish player at Player_1_Start replace the "X" with "1". Then replace the "Y" with a "1", "2", or "3". Here is a example for the skirmish player at Player_3_Start with building number two: Player3 Garrison2

Remember that each skirmish player can garrison up to three buildings. Any buildings named "PlayerX Garrison4" may not be garrisoned.

Way cool Pi!
I was wondering about that because of a topic in the maps and mods section.
Good to know!