Go to the building with hay bails. There is a hay cart next to it.

Jump onto the rear of the haycart, jump to the small bit of fence attached to the hay building, jump onto hay building.

You can now also jump to the army truck (towards the center of map) and off that onto a narrow ledge of the building next to it.

Also, climb 'Cantina' stairs, jump out window onto Cantina sign (quite hard to do sometimes) turn left, jump onto side roof of Cantina.