start by making arched doorways. And the doorways are higher than the wall segments You can see here the wall segments on each side of the doorway. Those wall segments are the standard 2.5 inches in height.

You can make simple arches or you can get a bit fancy with them like I did. Mine are stepped at different depths. It gives it a really good gothic look.

The Gothic Architecture template is here' It has the arches, doorways and buttresses and more for you: You can download it right here (pdf)

And make yourself some buttresses. These are not foam. You can use foam board or cardboard for these. They are thin! So, foam isn't a good option for them.

Glue the three parts of each buttress together then you can set them up right against the wall sections.

For the stained glass window over the doorway I first made a wall out of foam and cut out the doorway and circular window holes.

Then I covered the circular window hole with clear plastic and painted that plastic red.

Then I cut out the arch and window framework on foamboard and glued it over the whole foam wall. This arch and window pattern is in the template I give you.

Let's Continue and I will show you how to paint it all so it looks like marble