the leak that has been fixed. I would attempt to get the contractor or builder to finish the job and clean out the mildew, or whatever is smelling as a result of the initial leak. Fixing the leak is only half the job.
You almost have to open the walls up to find out the problem. You could have wet isulation, wall board, and who knows what else.
If the builder does not want to assist you which I am sure he/she won't, then if you do not want to tear out a wall at first, then try this:
Get a drywalls aw and cut out a nice neat circle or square. A small one will do. Then pour alot of baking soda into the hole. this will absorb the odor. Now, one other problem, you have studs every 16inches or 24 inches. Your challenge is to find the right cavity where the smell is.