You add the build tag to the topic NOT the TOC item. Right
click the topic and select Properties. Click on the Advanced tab
and there you'll find both content and topic level tags. Content
level tags apply to the content in the topic but not the topic
itself. If you want the whole topic to be suppressed the tag must
be applied at the topic level. Once you've done this, use the
single source layout to suppress the build tag you have
applied.