How many plaintiffs are required for a class action in regarding to failure to provide contractual item in regard to building residential homes

Generally, a class action is filed when you can not identify the specific individuals involved, and there are a number of individuals with the same legal problem.  There is no numerical limit, the court needs to find that the most important issues are common to all plaintiffs, and any issues that are not in common are not very substantial. For example, if an internet provider had a standard contract that said they could charge the customers $0.10 per minute of use, and instead, due to a computer error, charged each of its customers $.11 per minute,  instead of having thousands of customers file suit, a court would likely allow a class action to proceed.  On the other hand, in your case, the builder had separate contracts with a variety of homeowners, and the damages suffered by each homeowner were different, it might not be appropriate for a class action.