SQL Server 2008 R2 performance monitor metrics

Hi ,

I intend to monitor the performance of SQL Server 2008 R2 and raise alerts on the same for Warning and Critical conditions.

However , I am not able to find any bench mark values for the following parameters:

Server Metric:

It would be great if I could get something like- CPU% >85  is Warning and > 90 is Critical.  Are there other critical parameters that needs to be monitored ,that I am missing in the above list ?

Thanks