I didn't make it!
Ok, I'm just using the tutorial.scenario file to see how easy is it to create a custom UI. I've set all the camera points, written the hsc script for the camera, deleted all netgame tags, player locations and vehicles, then compiled the scripts and saved the scenario in Sapien. How is it, then, that after I build a cache file, and test it, the camera is stuck in 1 place, and there is no interface to use??? (PS, I know this makes it sound like I shouldn't be the leader of a modding/mapping team, but hey, nobody's perfect.)
What you could to is take a look at the tags in the original UI file (you can extract them with HEK+) and make sure the stuff seems similar. I don't do much custom UI creation, but most of the things I've learned have been through simply researching already created tags and figuring out how those work.