We had this problem - 33 flying squirrels! They are little and they had bred a couple of generations in the insulation of the attic. They were so quiet because they slept during the day and were outside at night, so we didn't know for quite a while.
Get a trap (Hav-a-Heart is one brand) at the hardware store. They can be tricky to set so have the manager show you. There are 2 sizes, so it helps if you know what you have in the attic. One size is for mice, flying squirrels and even red squirrels. The next size up is for gray squirrels but will work for red squirrels.
We used peanuts as bait - you can put them on the "trigger" panel loose, but if it's easier, stick them on with a little peanut butter. Once you get someone in the trap, you'll hear it! Get it out of the attic though - in this cold, they can die in the trap overnight. We put our little friends in the basement overnight, then drove them to a nature area FAR AWAY. That is key - they can find their way "home" from 5 miles away so.... We learned this from our pest control guy.
Be aware that releasing these animals is illegal - you are supposed to drown them in a bucket of water. But we couldn't bring ourselves to do this, so we went to the nature areas and released them anyway. There are some nature sanctuaries that will take them - and our pest guy had a convent that wanted them, and put out all kinds of feeders! So they had a happy home with all their buddies.
But absolutely call your roofer to have him find the opening. If one critter found a home, others will. However, if your guest is something little like a mouse, it may not be the roofer's fault - they can find their way in thru the little spaces around pipes. There are one-way exits that the roofer or pest guy can set up so the squirrel can get out but not back in - but the trick is, you have to know for sure that he has gone out. You also have to be sure there are no babies in there!
Have a REALLY good time with this...!!! LOL