The stoneworker need to be improvement, what is the point of make and structure research the upgrades and then destroy it? I Think that siege materials (the only upgrade that require the building) and reduce the cost of buildings by 20% is not enought, this force players to destroy the building because a economy building give you more advantage, especially if you are under siege and you produce all the resources inside the fortress, on the other hand, the moment you most need this building is when you are under siege. for this reason i think this building must give resources, maybe a upgrade that allow the stoneworker to produce resources or something like that... or the building can have some units to recruit, i was thinking that could be a nice idea that you can make a builder and this builder can construct anywhere in the map outside of the fortress a tower or statue like old bfme (then the builder disappears after the building is done) and you can only habe max 3 buildings by this way. I dont think it is a insane idea or unbalance (With an adequate price) since Gondor like you can see in the mod built towers and statues all over Middle Earth.
What do you think?
sorry my inglish and have a good day