<p>I have mixed views about commercial class libraries. Am I better off using a commercial  class library or starting  from scratch? If buying a library is the way forward which one for a C# developer?</p>

Put a value on your time, say $30 an hour.  Estimate how long it would take you to write the library, then add two times that for debugging and testing.  Subtract the time it's going to take you to learn how to use the commercial library with the given documentation.  Multiply by your hourly rate.  Compare.
Writing a library can be fun and rewarding, but "not invented here" syndrome keeps a lot of companies from creating anything useful, as they're stuck reinventing the wheel for additional cost.  Make sure it is extensible (if you don't get access to the source) and has what you need.  Buy it.
As a personal project, it's probably worth writing it from scratch at least once to see what you can learn, but on company dime you need to be productive and efficient.
Or write it from scratch and release it open source ;)