Convert the day of your birth to Roman numerals. This will never be any higher than "31" and will never be any lower than "1." This means it will be somewhere in between I and XXXI, or one through 31.
Convert the month of your birthday to a Roman numeral. This will be anywhere from I to XII, or one through 12, depending on the month -- "I" being January and "XII" being December.
Convert the year you were born into roman numerals. This is the trickiest part because it is a much higher numeral. For example, 1980 would be written as if it were one-thousand nine-hundred and eighty. This would yield MCMLXXX, or "M" for a thousand, "CM" for 900 and "LXXX" for 80. If you do not want to try to count out the exact number of your Roman numeral year, you can use an online Roman numeral converter.