Configuring MS SQL Server system databases - best practices?

Hi,

I need some advices and best practices regarding the size of MS SQL Server system databases. We use MS SQL Server for few services for our product and we provide to the clients sizing for production databases. Now we have a request to provide sizing for MS SQL system databases. How to accomplish that, on what facts? Some recommendations are that master,msdb,model and resource could be configured by default but the size of tempdb is affecting the performance system I should be consider properly.

Is there any documentation regarding this topic or some useful links?

Thanks. Best Regards.