is there a chart showing which way the air flow should be for case fans?

I am looking to add more to a new system I am building and I wanted some ideas to make sure I am getting the maximum air flow to keep my system cool as possible

Is it a good idea to modify a case to add more fans to it?

This case currently can hold 2 front case fans 1 side intake fan 1 rear fan with 2 built into the PSU - all fans but 1 on the PSU are 80mm

Hi Corwin,
this might be helpful. you should decide if you want to have a negative pressure flow, or a positive pressure flow. each has its advantages
http://www.xoxide.com/computer-cooling.html