Since they removed the outhouse from the stables, which was used to get on top of the roof I wanted to get up there still. so I decided to try the mammoth mount clip through walls thing and it worked to my surprise. Don't know if it's been posted before though
First you need to go into the corner I have circled in this picture and make sure your toon is up against the wall of the stables.
Next, hop on your mammoth and wait until your camera looks like this while facing the building.
Now press the button '/' on your numpad to toggle walking. Now aim your toon towards the corner you were facing at the beginning and keep walking forward and jumping until you are on the roof.
Enjoy