Need help with roofing

I get what you're trying to do. You're trying to get this effect, right?

https://www.ricordius.com/sims4/hallow/kh02.jpg

If you don't mind that the tops of some of the roofs are not a perfect flat floor, maybe the roofing on this build could help with some ideas. The link is here: King's Hallow; feel free to pick it apart. (I did try to explain how it was done, originally, but trying to say it in words just seems confusing.)

Alternatively, there's nothing wrong with using the half wall and leaving a hole in the centre. I'd pave that "hole" and call it a widow's walk or a rooftop patio....