Said code can be found here
http://stackoverflow.com/questions/12967896/converting-integers-to-roman-numerals-java
So I tried to port one from JavaScript into GML
Here's the code
http://pastebin.com/DWnRSAgZ
Obligatory GIF showing how it works.

NOTE: Take in mind that this will only work with a number between 1 and 3999
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Edited by: Gate, Aug 6th, 2016 @ 1:43 am