I haven't posted on this forum pretty much ever, although I have been practicing for a while, so this is new for me.

I thought I would put together a visual on common places where people bruise when rolling. I know when I was learning to roll, I kept bruising myself every time I tried the roll on concrete, and it took a while of trial and error to solve the problem. I assume others, especially those starting out, have similar problems with the roll, so I put this diagram together to help.
The areas marked in red are areas I commonly bruised myself when I was still learning proper technique to the roll. However, in a roll with correct technique, all of these areas will not come in direct contact with the surface, eliminating the potential for bruising.
The green line is just a generalization of where your back is making contact with the ground. Note, this is showing a roll where you are tucking with the right shoulder, obviously... so if you tuck the left shoulder, just reverse everything.

If you have not done so already, I would suggest looking at the roll tutorial (
http://www.americanparkour.com/content/view/264/177/) because I am assuming you already understand the basic principles of the roll.
The first area I commonly bruised was the red area on the shoulder, which is the scapula. If you are bruising this area, you are most likely not tucking enough going into your roll. You should land below and to the left of the scapula, on the muscular part of your back. In addition to the tucking, I found that an exaggerated sweeping of the right arm towards the left leg helped immensely to solve the shoulder bruising problem.
Also, I found that one of the vertebrae in the lower back sticks out when in a hunched (or roll) position. On the pelvis, the inner edge is also easily bruised as it sticks out. If you are bruising any of these points, it means that your roll is not diagonal enough across your back.
Finally, the top portion of the femur, right below the hip can also bruise when finishing a roll. You want to be coming out of the roll on the outer meaty part of your butt, making sure to no make surface contact with the bone.
I am sure you can bruise alot more areas if your roll is a mess, but I can't help if you are doing a belly flop, or face plant etc.

I hope this helps anyone who is having trouble with the roll. Later.