Roof replacement during the winter is the best time.
One advantage to roofing in winter is that homeowners can pick from pretty much any roofing company to install their roof, as most are not too busy during this time of the year. When installing asphalt composite shingles, manufacturers do not change their warranties based on installation temperature. They offer the same exact warranty as a roof installed at any other time of the year.
Of course, new shingles need to undergo thermal sealing, which can take several days and even weeks in temperatures of 40 degrees Fahrenheit or higher. Another positive point is that roofing material prices will be cheaper in the winter months.