I had to sandpaper the thick cement glue so there will be no marks on the joints between he foam boards.
I also sandpapered the foam board itself to help the white glue stick to it.
Cleaning the board from any particles.
After placing the cathedral on the board lines were drawn around it to help placing it centered to its right place during the upcoming steps.
These marks will be useful later so no rocks will be glued where the building is to be fixed.
The wooden dowels previously installed under the building have left some marks on the foam board. A long drill bit was then used to drill through both the foam and the wood base.
A larger drill bit was finally used to drill a chamfer under the wood base.