Go to the BP_BuildMaster then go to the event graph then the place the arrow is pointing to in this image.

Then make the changes shown in the image below.

Go to the Get Overlapping Actors function and delete the highlighted nodes shown in the image below.

Then in the same function change the change the target of the node in the image to the SelectedMesh component like in the image below.

Then in the same function make the changes shown in the image below.

Next go to the Collision function and change the return node input to disabled.

Then go to the Create Foundation Grid function and add the highlighted nodes shown in the image below. Do this in the first loop in the function.