Creepy shadow on the roof?

[Unforgiven]

Me and my boyfriend were coming home from the mall. We were across the street a few houses from his but we clearly saw a man standing on his the roof of his house. I was not even a man it was more like a really black shadow darker then the sky and we both saw it. My BF asked what was his dad doing on the roof at this time when it was dark. And to me when i saw it it seem to be looking up at the sky. A soon as we got to the other side of the street and we were entering his driveway the shadow was gone but my boyfriend said he saw it scurring away. When we went inside his parents where there and we asked them if either one of them were on the roof and his dad said no. Soon we all went outside to do a quick search around the property and made sure no one was around. The weird thing was that my boyfriend said that the person scurred away like if it wAS hiding from us. and another thing is that he has two dogs that did not even bark which was weird because they are very alert. Now the reason we are a little freaked out is because a few months back My bf said he saw a white shadow. But he only caught the (legs of a person) out of the corner of his eye crawling into his room. (Sort of like the spider man position when he is crawling up the buildings) only he caught the shadow out of the corner of his eye crawling on the floor into his room.
SO has anyone had any experiences similar and is it something we should be worried about? or does it mean something ?

thx for your hellp !