Using a Variable Currency based building model - trigger

[KmLocco1666]

I'm have trouble with making a trigger function, I wanna make a building with a new form of currency (Using Variables) but when a buildings Structure(Blacksmith) is being click on (or about to be constructed) and i want it to stop the unit from being able to build the structure. for not having enough of the new form of currency.

How would i go about this?

Or if someone could point me in the right direction, to get some insight on this subject.

 

[Unregret]

Here you go:
1. Custom Resources 1.30

2. Custom ResourcesCost

 

[Dr Super Good]

I am not sure it is possible to prevent the player from trying to place the foundation, however you can stop the foundation being built.