I don’t know how to do it, but In the map derailed there is a way for the fireteam to get onto the rooftop of the train yard big blue building. They were using the big round metal vents at one of the corners of the exterior of the building to do it.
I figure it’s not intended for the fireteam to get up there so I wanted to bring it to your attention. Hopefully what little details I provided can help you reproduce it to fix it.