Need help with a multiple building problem

[Chopzz]

I have a building which produces lumber when build and players can only build one of them.
But i want it to be upgradeable. the down side of that is that when a player upgrades it they can build another that is not upgraded and continue in a loop. How do i fix that?

Thanks in advance

 

[VadamLoke]

Although there are more ways to do this, i think the easiest one is to:
Limit the construction of first building to 1, disable construction availability when it finishes construction and allow construction in case any of the buildings dies

 

[Chopzz]

Thanks alot! Never even thought of that haha