Chain Fence to separate roofs

I live in a 4 floor, 8 apartment condo with a flat roof and our issue is people walking on our roof from the two adjacent rental buildings. We would like to put up a chain link fence on both sides to keep people out. I’ve seen a few around but I’m not sure how legal they are and if there are any limitation on hight (including the nights of the parapets we have on the two sides). Also would this be a job we can do without permits or would we need to do everything through the DOB? Any roofer with any experience in this forum that could help us out and come for a quote?