Good locations for rocket jumping:
There are a lot. Starting with control point A, defenders can cover both exits from on high. On the left, you can get up onto the cliff from the roof of the small hut, and from the right you can jump up onto the tall lamp post on the barbed wire fence from the ramp.
There are 3 places inside the control point building. The lowest one is great for attackers since you are low enough to capture the point, while the other two are too high but offer superior vision and cover respectively.
Also just outside the capture zone, you can make your way to the top of the little walkway that goes off the map. Although quite exposed and visible, it’s also very high.
On to point B. Defenders can once again cover the entrances from the cliffs. The left side is easy enough, with an outcrop just beside the concrete exit, while on the right one must be at something of an angle from the doorway. This however allows you to shoot inside the corridor.
A great place for both attackers and defenders is on top of the roof at B. Looking down through the windows allows for deadly sneak attacks on unsuspecting enemies inside the capture zone, either attack or defending it. See tips for how this can best be reached by attackers.
Two nice little places, especially for demomen preventing the passage of defenders to B, are the rafters in the rooms between C and B. It’s impossible for the enemy to see you without being in an area you can cover with sticky bombs.
C has defensive positions above all the exits from A and B, the simple ones being the pairs of lights that hang from the doorways, as well as a tall lamp post next to the near entrance from B.
In addition, defenders can perch themselves right up next to the laser cannon on both sides (but not the front) of the tower roof, giving a great view of the ground below.