Army officer engaging a second person to make plan (6)
I believe the answer is:
Here is my best explanation:
'plan' is the definition.
(layout is a kind of plan)
'army officer engaging a second person' is the subsidiary indication.
'army officer' becomes 'lt' (I've seen this in other clues).
'engaging' means one lot of letters goes inside another.
'second person' becomes 'you' (I've seen this before).
'lt' placed around 'ayou' is 'layout'.
'to make' is the link.
(Other definitions for layout that I've seen before include "Arrangement of a printed page", "Arrangement of text and pictures on a page" and "Arrangement of page, buildings, etc".)