Give whatever warranty you want. I've got a sliding target that really depends on what the project is. For some things it's going to be a year, some it might be 10 years. Others lifetime on labor- I don't have a problem warrantying my labor for the life of the building- but that doesn't mean I will warranty the materials. Materials are warranted for the same guarantee as the manufacturer will give for the application.
But- it's a really good idea to look at to see if and what your state has legislated. Some don't have any legal minimums, some can be quite long, much longer than the standard 1 year.