The most common and most likely answer to this crossword clue is the 8 letter word BIRETTAS
I've seen this crossword clue in The Daily Telegraph
B
I
R
E
T
T
A
S
More clues leading to the result BIRETTAS
Buddy explains!

The straight part
We know that "tiles in church" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tiles in church = birettas.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BIRETTAS mean?
BIRETTAS noun- A square cap, originally with four ridges across the top, surmounted by a tuft, worn by Roman Catholic clergy (and by some in the Anglican Church). A three-sided biretta is worn by Roman Catholic clergy for liturgical celebrations.