National Homes Lakeshore

We moved into our National Home three years ago. We had a major issue with the foundation at the time it was built, which National tried to dismiss as not a big deal. After notifying Oakville's inspector, the Town of Oakville sided with us, there was an engineering report, and the foundation was fixed. We moved in, and everything seemed to be fine.
Recently, I noticed a drip from one of the vents, so we looked at the venting system in the attic and found a leak, and now there's mould growing in our attic. Of course, the Tarion warranty expired last year, and National has refused to stand behind its workmanship and fix it. National actually said roof leaks are due to wind, rain and bad summer weather. Isn't it unbelieveable that we paid more than a half million dollars for this home and the roof didn't last more than 3 years?
Between the foundation and now the mould issue, we regret making such a large purchase with National Homes. This is a company that takes a large amount of money and then can't stand behind its product or make it right for its customers.