Please make it possible to upgrade special event buildings after the event ends.
Many of the Special buildings gained during events are not upgradeable once the event ends.
Over time as players lvl up they are stuck with partialy upgraded buildings they gained from past events.
My Easter Residence from 2015 event will forever be at lvl5 (unless this suggestion is implemented)
A guildie friend has a lv2 Spacious Warehouse capacity at this lvl is just 3k, a lvl 6 one would be 48k
At the time of the event he was a new player under lvl 20, now he's already at lvl 54 but stuck with a build that potentially could be so much better that it is now + forever locked at 3k with no way to unlock it's 48k potential. (unless this suggestion is implemented)
Many other examples available.
Maybe,
Upgrades could be locked for 12 mths following events finish date.
Upgrades would only be possible during similar future events.
or whatever other restriction BB can come up with.