ayoye

i need help,when i play any map i've downloaded, in the imperial assault mod i don't see any building,i can only see the door of the building,and the ai teem don't build anything.i can't even build map for this mod with world builder beacause the files of the mod have the extention .mod,if i change the extention to .big,after i play it change back to .mod.how can i do map and modify the addon map i have to play in imperial assault.i tryed many things but nothing work.