Tailoring of spells is a standard part of Ars Magica. This is a rework of Conjuring the Mystic Tower to create a cathedral instead of a tower. As such it has the same mechanics but a different description.
Conjuring the House of the Gods
Creo Terram 35, R: Touch, D: Mom, T: Individual, Ritual
This spell creates a large cathedral, subject to the desires and designs of the caster. A typical layout has a broad central hall, several tall spires, many private chambers along all sides, stairways between levels, window spaces along all walls, a subterranean vault, and a smaller private chapel to one side.
Walls 1-3 feet thick at the base. The cathedral is bordered by a 1 pace tall wall set 10-15 paces from the outer edges of the church. The cathedral has room to accommodate hundreds of worshipers in the main hall, and their supporting staff dwellings, supplies and meeting places.
The spell provides 10,000 cubic paces of stone. The complexity modifier allows for the structure to be ornate, and made a single piece of stone with shutters, doors and such built in. When small parts are needed they are created within the single piece using thin stone slivers. The overall spell design has allowed for some internal and artistic complexity.
(Base 3 to create stone, +1 Touch, +4 size, +3 complex design, ritual)
Within the game where I hope the spell will be used there are many types of faith, with flexible design the same spell can create very different catherdrals, as long as the building is sufficiently church like. It would not be possible to use CtMT to create this style of building just like a spell to create a horse cannot create a dog.
Find this spell and hundreds more for Ars Magica in my grimoire.