Hi,
The custom scenery folder contains a folder named global airports.
Strangely enough, this is where are described all the buildings of every airport (in DSF files, organised by tiles of 1x1 degree of LATxLON.
Anyway.
Running the installer should bring you back this folder (and about 10 others) which are actually part of the default install.
I am not sure.. confirm this is what you have done already, and the buildings are still missing?