We have a couple of tags on the main site that are semantically similar, but are generally being used in different ways:
At the moment, questions tagged "Building" are all about building techniques, "how do I build..." type questions, while questions tagged "Design" are generally used on questions about set/element design which I think is correct.
However some questions that are more about building a particular model have been tagged "design" as in "How do I design a mechanism to do this".
Should we make design a synonym of building?
Should we keep them separate and update the wiki on design to be more explicit about the use of this, state that if your question is about a MOC it should be tagged building?