You have to launch yourself to the roof using the double barrel shotguns charge shot!
Ahh I see! How can I obtain the shotgun? I've only been using the revolver so far. Thank you for your help!
I'm also stuck, I feel like I've searched the whole map for something
Edit:
Just found it, if you go straight but take the leftmost path from the saloon, then keep going until you see a door on your right with lanterns
