I think this has been suggested a number of times and the developers have said they don't want to do it. Rather, they want us to remove buildings and replace them with other buildings, either as we unlock new technologies or gain them in events. Having to move things around and choose what to replace is apparently part of the challenge they want us to undertake.
In some ways I'd like to have a storage option, but I can also see their point about that making things a little too easy. For example, sometimes I build level 1 armories temporarily at night to set troop production, then knock them down and replace them with level 2 workshops to produce supplies. If I had storage, I wouldn't even have to spend resources and time doing that. I could just put all my workshops into storage and plop in my armories and vice versa. in fact, I could have fully leveled armories that I only put in for 5 minutes twice a day to set troop productions, switching them out with fully leveled workshops.
An alternative would be to make the storage only available for buildings won in events, but I imagine there would be ways to use that to gain unintended advantages.
Overall it seems like this would defeat the purpose of some of the limitations intentionally built into the game.