TeamLava is aware of the problem. They have not given us a time table for the fix.
The Valentine's version of the game always shows the correct requirements, so you can use that game to see what they are. If you have deleted the Valentine's version from your device, you can redownload it from the App Store (look in the purchased tab).
if you started playing after the Valentine's version was removed from the App Store, and force closing the game does not solve the problem, you can check the requirements for most building in the spreadsheet linked in this thread.