The custom building used for commercial purposes was especially interesting, primarily because of the inherent flexibility she could use it with.
Except for the requirement that a unit must have at least one room to be used as a residence (a limitation to her custom building), everything else would be entirely up to them. They could choose whether to use a floor, or the whole building, or even just a room, for business.
In fact, she had already seen something like this, where they chose to designate a single room adjacent to the street. People would just go to this 'take out window' and go on their way.
Everything was all done very easily too. One option was for the citizens to just go to the building they hoped to use (assuming it was unowned) and the window for rental or purchase will appear.
Indeed, if you have money, invest in real estate!