Roi Tracking options and open source scripts

I need your advise!

[Controlia]

Hi everybody,

We are a SEO&SEM company, we plan to develop our own ROI tracking platform. I would like to have your feedback on two issues:

1- What do you consider the most important information and options a Roi tracking service should offer?

2 - Could you reccommend me some good open source roi tracking scripts?

Thx for your help

[Controlia]

any help? please