Desert Operations Guide: War Indemnity:

Here it depends of how much the loser lost from his attacks-value (resp. from the defence-value) lost from his troops.

Example:

100% loss of Attack-/Defence- value = 33% loss of buildings.

1% loss of Attack-/Defence- value = 0,33% loss of buildings.

50% loss of Attack-/Defence-value = 16,5% loss of buildings.

So you can calculate other extension stage

Special cases

No rules without exception, therefore here are some: If there's no battle, because the defender has no units, this will be treated as loss for the defender with a 100% loss and (33% loss of buildings). If there's no battle because the different units can't attack each other (resp.: Attacker: M1A2 Abram, Defender: Water-mine), so it will be clarified in the profile statics as a victory, but nobody will lose any buildings nor will there be navy units destroyed. If both lose 100%, the attacker will be treated as the winner and gets 33% of the opponent’s buildings.