Plan building great sty (8)
I believe the answer is:
strategy
'plan' is the definition.
(strategy is a kind of plan)
'building great sty' is the wordplay.
'building' is an anagram indicator.
'great'+'sty'='greatsty'
'greatsty' with letters rearranged gives 'STRATEGY'.
(Other definitions for strategy that I've seen before include "Scheme" , "Systematic plan of action" , "Plan or policy as for conducting campaign" , "Approach" , "Plan for achieving a particular long-term aim" .)