There are very few restrictions on Romulan naming conventions. Obviously, we would prefer if they were not too human-like, or derived from non-thematic sources. We expect some form of creativity, but if originality is a problem, there are sources to assist you, such as the Romulan dictionary, and the Rihannsu Word Generator, as found on TOS TrekMUSE.
A sidenote however: You will encounter two primary styles of names. Modern Rihannsu names are the most common, especially as time goes on. You will come across the occasional S'**** name however (ie: S'Kurn, S'Kard, S'rah), and it may throw you for a loop if you've read up on the language structure. These names defy the normal language rules, but they are sourced from ancient tradition. Many of these names are in honorable reference to the Ship Travelers that left Vulcan and founded the new Rihannsu society. In many cases, these are not birth names in modern (TOS) times, but given names for individuals who have been adopted into other houses at early ages.
The above applies, of course, to a Romulan firstname. Romulans generally have four names: A first name, which their parents give them. A second name which reflects the area or city in which they were born. A house name, which is like a last name. Last, but not least is the 'rehei' which is a secret name, found by the individual, and known only to themselves and their closest friends or relatives. Adding a rival house to your name or using a house name as a first name is not recommended, your parents most likely would die before naming you such. Romulans place great emphasis on the whys and hows of names, therefore, you should take care in picking out your name. Names are not taken lightly in Romulan culture.