SOP - Available Capacity for Material

HI

I am working on SOP (Sales and Operation Planning). I have created rough cut planning profile in which i have used material as resource. Whenever i m checking capacity situation system is showing the correct capacity requirement i.e. correct material., but available capacity is 0. Can anyone please tell me why it showing zero and how i will get the exact figure for that Material resource.

Regards,

Anand.