The most common and most likely answer to this crossword clue is the 8 letter word PREFORMS
I've seen this crossword clue in The Times
P
R
E
F
O
R
M
S
Buddy explains!

The straight part
We know that "shapes in advance" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case shapes in advance = preforms.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.
Crossword Answer definitions
PREFORMS noun- An object that has undergone preliminary shaping but is not yet in its final form.
- The rough, incomplete and unused basic form of a stone tool.
- A word that is no longer in use, but has been reconstructed from current ones.
- To shape something before some other operation.