All buildings are the same for a culture. When you construct a building the version for your culture is automatically built. Unless you can code different factions to get different building upgrades all the buildings will look the same (this won't cause a recruitment problem because factions can recruit from buildings they can't construct).

Could someone test whether the following code would work (I abbreviated this because I don't want to research the exact info).

##Building 1
#Faction (Bretonnia, Chaos)
#Building info
#Units: basic (Bretonnia, Chaos)
#Building upgrades: Type A, Type B
##Type A
#Faction (Bretonnia)
#Building info
#Units: basic (Bretonnia, Chaos), medium (Bretonnia), basic (chaos)
##Type B
#Faction (Chaos)
#Building info
#Units: basic (Bretonnia, Chaos), medium (chaos), basic (Bretonnia)