Legal Question in Real Estate Law in California

It depends on when you knew or should have known that they failed to disclose the leaks. The problem you have is two-fold. 1. If the tampering is "obvious" then the clock started ticking when you bought the house and may have run out three years later, although you could try too get a good lawyer to make a case that a four-year limitations period applies. 2. The leaks didn't start the first winter you owned the house. Roofs don't last forever. Patches to previous leaks (which may be what you call "tampering") may last almost as long. So the roof may have been properly patched by an owner before the one you bought from, and the seller to you may well truly have known nothing about it. In that case, you wouldn't have a case at all.