How to write the number zero in Roman numerals?

Answer:

The zero can not be interpreted in Roman numerals, because however advanced the Romans were for its time, they had not conceptualized the existence of a number that interpreted the nothing, that is to say the zero.

Ancient Rome stood out more for its architecture, its political system and above all for its code of laws. But as for mathematics, the Arabs, Egyptians, even Greeks, were superior. And even today, it is argued that the first civilization of antiquity to use the number zero were the Mayans.

Why does not the number zero exist in Romans?

Because the conception of zero was not incorporated in the numbering systems of the Mediterranean civilizations.
Although the notion of "nothing" or "no" element existed, it was not considered necessary to have a special symbol since the numbering system was non-positional and additive and each number had a special symbol to name it.
Zero became necessary at a time when some civilizations (such as Hindu and Maya) used positional (though primitive) counting systems that required a "vacuum" between one order of magnitude and another (as in our current system Decimal, where 403 indicates that 4 has a value of 100, that there is no value for position 10 and that there are 3 additional units).