It's lovely having all these buildings that can now be upgraded to level 6, but on discussing this with a friend, we feel BB are likely missing out on a gems opportunity.
There are many people who would love to upgrade their Provision House or their Barracks, but the thought of waiting 7 days is off-putting, and the cost in gems expensive.
The alternative idea here is to set the upgrade off using the resources stated (granite and grout for instance), but at any point during that time have the option to fast-track the remaining time using gems but on a scaled down cost.
For example if it costs 7000 gems to upgrade 100%, and the building had already gone through 5 days in the resource cost option, allow the player to spend just 2000 gems to fast track it for the last 2 days.
Of course to keep it simple, if you opted to do this, you would still lose the initial resources, but at least the choice would be there.
I believe there are many more who would use this system rather than pay outright for a full 7 days with gems, so I think there is some value for BB to look into this as a future option.
Apologies if this has been suggested before, but if so I think it deserves a prod in BBs direction again