You might see them atop a house with hand in knickers (8)
I believe the answer is:
pantiles
'you might see them atop a house' is the definition.
(type of roof tiles)
'hand in knickers' is the wordplay.
'hand' becomes 'ile' (I am not sure about this - if you are sure you should believe this answer much more).
'in' indicates putting letters inside.
'knickers' becomes 'pants' (synonyms).
'ile' going within 'pants' is 'PANTILES'.
'with' is the link.
Can you help me to learn more?
(Another definition for pantiles that I've seen is " topping for the house".)