What about a raceDAY CB? We could have a dio (obviously a huge one) that's a racetrack! And the builds pretty much have no limits. Vendor booths, grandstands, people of course, trucks with trailers, media coverage, the pits- that'd be so cool. My grandpa had a train dio in his garage, and anyone in the neighborhood could add to it.
Of course a scale would have to be agreed upon, but that shouldn't stop an idea like this, it would be epic.