double check the resources. are they delivered to the building location? you didn't confuse iron ore with iron by chance? is there access to the building site,other side of river with no bridge,etc?
when you click each builder and then click the "tools" icon in the top right where does that builder point to? oh and i doubt you did this but did you oause the building? i do pause if i need the builder elsewhere or am low on a certain material.
There's nothing the modkit can do to change the behavior of the citizens. The AI for them is hidden from us. Only the core game itself can tell the citizens what to do and where to go.
Try reducing the number of builders to zero and then a bit later bring it back up to however many you want.
I have had this happen when I assign laborers to clear some patch of land. They are the ones that deliver the resources to the building site not the builders, so if they have been assigned something else to do, you have to wait until they are done. Or you can increase the priority for your building and they will deliver resources, then your builders will build it.
In an instance where this is happening, you can usually sort it out by highlighting the building site with the priority tool. Some folks have a habit of doing so a couple times in a row to emphasize to the AI, "Hey you fools, come do this thing now!"
