Been on these forums for awhile now, and I finally get to contribute for the first time, if you need to criticize, at least make it constructive.
Found a way to get on top of the building beside the IF Bank.
You will need to mount up underneath the doorway (you need a mammoth for it to work) and face towards the arrow, then you will jump up while every slowly moving in the right direction, make sure you jump so that you're jumping inside the wall, so that you don't fall into the building or outside, or worse falling through the world.
Took me a few tries to get it, but i don't believe this is a repost, been on the forums for quite some time now. GL =]