Well let's say a trade for Durant costs
Bos sends : Lee(15 mil expiring) , Crowder , 3 brk picks
OKC sends: Durant
That leaves us with a roster of
PG: IT / Rozier
SG: Smart / AB
SF: Durant / Turner
PF: Amir / KO
C: Sully / Zeller
I think this team could reach the conference finals, but lose to Cle in 6.
1)We would still have the Dallas pick , maybe Minny pick , and our own picks to fill out the roster.
2) We would have the cap room to sign Durant and another max player, maybe two (Horford, Whiteside, Mike Conley are all UFA in 2016).
I don't know if a core of Durant , Horford and Conley could win a finals ,but it would be a fun team for sure .
PG: Conley / IT
SG: Smart / AB
SF: Durant / Hunter
PF: Amir / KO
C: Horford / Vet min
But this team would likely only have a 5 year window to be competing for a title , much like the KG era.
Looking at it like this , I would rather keep building through the draft and try to just sign Durant outright , then we could use those picks to trade for players to add around Durant.