Hi, I did this once but as im not sure what type of hutch you have i dont know whether it will be relevent to you.
The hutch had 18" legs i got two 6 inch thick legths of wood and raised the hutch to the same height as the run and then all i had to do was bolt the run to the legs (legs where 44x44mm square) i then got plywood screwed to back and sides to meet the floor. I think the total cost was around £17 its not as complicated as it may sound either. i also added a 1.3 metre ramp which was made from remaining ply.
hope it helps or at least gives you and idea.
Jason