Like the others have said, check foundations. Find the cause first and
then remedy it. Go to your local home builders assn. Ask them for
advice. There may even be some Gc's or sub's there between jobs. I'd
take the time now to consider extending the basement. It'll give you
the extra space down there as well. Once the floors are releveled,
insist the contractor "mothers" all floor joists. That means studs
are added to each joist for it's full length. It increases their
structural capacity. You shouldn't have a problem after that .