Interesting … Most class-action lawsuits are opt-out, meaning you’re automatically a member of the class unless you take action to remove yourself.
Two risks:
(1) Very rarely, you may be liable for legal costs if the suit is lost
(2) If you receive a settlement, it generally comes with a liability waiver — you can no longer sue the builder on your own for the problems with your house. What kind of costs are we talking about to fix the plumbing design error and other shortcuts?