Open-top car seen in roll without notice (8)
I believe the answer is:
Here is my best explanation:
'open-top car' is the definition.
'roll without notice' is the subsidiary indication.
'roll' becomes 'roster' ('roster' can be a synonym of 'roll'**).
'without' is an insertion indicator.
'notice' becomes 'ad'.
'roster' going around 'ad' is 'roadster'.
'seen in' is the link.
(Other definitions for roadster that I've seen before include "Open-topped car", "Small open-top car", "An open car without rear seats" and "Open two-seater car".)