This is one of those things that sounds so mundane until it actually happens to you and then you can't stop thinking about it. What kind of sound was it exactly - was it rhythmic like footsteps or more random? And how heavy did it seem?
I ask because I read something a while back about "roof walkers" being reported in a few different countries, basically humanoid figures seen on top of buildings at night. No idea if theres any solid documentation on it but the accounts pop up fairly regularly on here and on reddit.
Also worth ruling out thermal expansion if you have a metal roof, that can make some genuinely weird creaking and shifting sounds after dark when temperatures drop. But if it genuinely sounded like something moving with weight and purpose then yeah that's a different thing entirely and I'd want more details.