UPDATE (5/26):

The beta of the citadel on the Capitoline (a work in progress):



UPDATE (5/27):

I have created an introductory tutorial in the Tutorials subforum, explaining how to edit ground features which is the basic building block when creating custom cities. The tutorial can be found here:
https://forums.totalwar.org/vb/showthread.php?t=48365

In other news, with the creation of the first tutorial I would like to organize a group of modders together, people who are interested in creating new cities, to facilitate exchange of information and for collaboration and group work.

I am considering a few names for the name of the guild, such as The Crafters Guild or The Masons Guild. I would also like to think of some names that don't have the word "guild" which has medieval connotations. In any case, PM me if you would like to join and are following along the tutorial and are seriously interested in pursuing this.