press button with and have confirm unity
IEnumerator PlaceBuilding()
{
// whatever you're doing now with the temporary / placement preview building
ConfirmationDialog dialog = ShowConfirmationDialog(); // instantiate the UI dialog box
while(dialog.result == DialogResult.None)
yield return null; // wait
if(dialog.result == DialogResult.Yes)
{
// place the real building
}
else if(dialog.result == DialogResult.Cancel)
{
// remove the temporary / preview building
}
}