How to let a user select a profile while registration?

Hi,

I've 3 roles and would like a user to select his or her role / profile while registration in one of these three:
1. Student
2. Professional
3. Self Employed

I created these roles and assigned them proper rights, but not able to understand how can a user select one these roles on his own, minimizing the website administrator work.

Kindly help
Thanks and Regards