Thanks mate we kinda worked that one out :p
The problem is as ripper998 highlighted (thanks for your post ripper :icon_eek:) there is no rubble to repair the building with......
ripper is right armoured random patrols come through the main base around the 6 hour mark with the tank and destroy the wreck and heli repair bays, no rubble remains for a rebuild
further thoughts? we can turn the random patrols off but it detracts from the realism :(