Ok, 4 tiles will be sufficient enough.
And I want to combine this exp with another one, based on both city walls and reconsctruction idea. Coming soon!
I kind of liked the idea of just doing the small mini expansion by itself. But I am still curious on what this other expansion will be!
I think the Builder should be a follower for itself in a CUC. If you have a normal follower, the big follower, wagon or mayor in the city, you can take it (all) back (but don't have to), if you place your Builder instead.
The builder may only be placed on the CUC tile, otherwise the normal rules apply to the builder. Once a CUC tile is added to a city or is by itself, no Meeple may go in or out until the CUC is complete.
Merging a city to a CUC: perhaps there could be a scoring like merging a farm with farmer to a farm with barn - the player with the city not under construction scores 1 point per tile (2 points with cathedral).
I like this idea! It fixes the issue of merging cities and how to handle them. Good job.
Merging 2 CsUC: Either they merge like to normal cities and majority of followers decides the ownership (Builder = 2?) or the bigger CUC takes the smaller CUC, the followers there go back to the player.
Merging CsUC should be merged like normal cities. This will be the only way to get more Meeple in. Builder should still count for one follower.