The height limits weren't actually legal, they were those of the materials and construction techniques available. Without the aid of steel beams to provide tensile strength and other modern techniques and materials, something around 200 feet tall is the limit of a brick structure before the ground floor is starting to approach solid wall over the entire footprint.
The reason is that while brick and wood make a structure very strong in compression, they are unable to provide the tensile strength needed for larger structures. This can be compensated for somewhat by filling in the base, converting some of the tensile load into compressive loads, but the walls at ground level are getting very thick at this point.
Certainly one can push the limits a bit in order to set a height record, but land has to be very, very, dear to justify the expense other than for bragging rights. Even then, adornments on the roof, similar to those designed late into the Empire State Building, are more effective in attaining increased height than extra stories.
However, this question then rapidly then becomes about strength of materials, architectural techniques, and other subjects beyond the scope of this site.
Update: Yes of course the Romans used a concrete similar to modern Portland cement; but without steel reinforcing bar that exhibits the same compressive strength and tensile weakness as any other masonry.
Update 2: Can 200 feet be related to stories?
Yes, and no. Ostensibly the 200 feet is roughly 20 stories, but there are two caveats:
1. That is assuming modern brick/concrete, which is significantly stronger than ancient Roman; and
2. Such a building (and I use the term loosely) would have a bottom half resembling the Great Pyramid, with an 8 or 9 or 10 story insula perched on top. Usable non-wall space in the bottom stories would be on the order of only 10 to 15% of footprint.
No sane landlord of any age would build such a structure as a money-making insula. However, if this is fantasy game research, make up some reason why the extra height is worth the prohibitive cost.
For example, the Great Pyramid topped out at about 480 feet originally.