The most common and most likely answer to this crossword clue is the 13 letter word MANUFACTURING
I've seen this crossword clue in The Guardian
M
A
N
U
F
A
C
T
U
R
I
N
G
Buddy explains!

The straight part
We know that "Devising" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case devising = manufacturing.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 MANUFACTURING mean?
MANUFACTURING verb- To make things, usually on a large scale, with tools and either physical labor or machinery.
- To work (raw or partly wrought materials) into suitable forms for use.
- To fabricate; to create false evidence to support a point.
- The transformation of raw materials into finished products, usually on a large scale.
- The industry in which such products are made.
- Used in manufacturing.