I was confused, I thought it had to be all boxes. I guess reading the descriptions is a good idea 
Sky Tower
A solution by Jonas P (Time: 0.8s, Blocks used: 1)
andyadmin added the Main Game Hard tag .
A solution by Ray 'BLJ' Duck (Time: 0.8s, Blocks used: 2)
A solution by Ray 'BLJ' Duck (Time: 0.7s, Blocks used: 3)
I won yeees
A solution by Cat (Time: 1.5s, Blocks used: 2)
A solution by Jab (Time: 1.5s, Blocks used: 15)
A solution by Tom (Time: 0.6s, Blocks used: 1)
A solution by Simon (Time: 1.5s, Blocks used: 8)
A solution by Maureen (Time: 1.4s, Blocks used: 6)
10 days later
A solution by Grandpa (Time: 1.5s, Blocks used: 5)
23 days later
A solution by cf (Time: 2.0s, Blocks used: +11)
Mine seems very different to everyone else's. Much more block spendy.
ColonelFazackerley But it has a surgical feel to it.