When I first looked up at the ceiling, I just stood there taking in all the detail trying to figure out what geometric or natural influence contributed to the design. The columns look like giant petrified trees leading up to jagged circular groups of geometric shapes.
I don’t think there is a flat surface anywhere inside the La Sagrada Familia. Well, except for the floor.
I used a 24mm lens with the image stabilisation turned on. A greater field of view, such as a 17mm or wider, would give you a broader view of the ceiling and could cover the stained glass windows on both ends. However, Canon do not make a wide angle lens with image stabilisation, well not professional versions, so I don’t use them for interiors.
I could use my 17mm with a high ISO but then 6400 or higher for interior details does not look good enough for me at 100%. If you are not concerned as much as I am with the 100% image quality then I would recommend a wide angle lens with high ISO to cover more of the ceiling.