The upper surface's outside of troop movement (7)
I believe the answer is:
rooftop
'the upper surface's' is the definition.
'rooftop' can be an answer for 'surface's' (rooftop is a kind of surface). I'm not sure about the 'the upper' bit.
'outside of troop movement' is the wordplay.
'outside' is an insertion indicator (some letters go outside others).
'movement' indicates anagramming the letters (letters move around).
'troop' is an anagram of 'rotop'.
'of' put within 'rotop' is 'ROOFTOP'.
Can you help me to learn more?
(Other definitions for rooftop that I've seen before include "may get slated?" , "Building's highest point" , "Highest point of house" , "Of Porto (anag.)" , "Elevated point" .)