Rolling in it is preposterous (4)
I believe the answer is:
rich
I believe this clue is a double definition.
'rolling in it' is the first definition.
(I've seen this in another clue)
'preposterous' is the second definition.
(rich can mean outrageous or unbelievable)
'is' is the link.
(Other definitions for rich that I've seen before include "Having many possessions" , "Of great worth or quality" , "having much wealth" , "Very amusing; wealthy" , "productive" .)