I found a simply way to get the AO file:
- search for the original F-16 roughmet DDS-files
- konvert these files to BMP (not sure this is required, but I do so)
- now the red channel is the AO file! Its a high contrast black and white map (see below)
Furthermore it is a bare file, without any markings, so it is an excellent AO template:
Not sure this works anytime and for any aircraft, but for the F-16 it does.
Now you just need to add the green layer (rough part of the F-16 template) and the blue layer (metall part of the F-16 template) and you finally get a proper roughmet file.