Main network housed in room at the top (8)
I believe the answer is:
atlantic
'main' is the definition.
(Atlantic is an example)
'network housed in room at the top' is the wordplay.
'network' becomes 'LAN' (Local Area Network).
'housed in' means one lot of letters goes inside another.
'room at the top' becomes 'attic' (room at the top of a house).
'lan' going within 'attic' is 'ATLANTIC'.
(Other definitions for atlantic that I've seen before include "Latin cat strangely in the sea" , "Tilt a can at the ocean" , "Sea between Old and New Worlds" , "Great sea" , "New Jersey resort" .)