Role Based Access to Content

Hello,

I have a sample code download page on my site and wish to grant access to content based on different roles.
e.g.
Let say
1. Role 'A' has view/download certain sample codes on the download page.
2. Role 'B' can view/download certain sample codes.
3. The basic 'authenticated user' should not be able to view/download this content.
4. Also Role 'A' user should not be able to view/download sample codes meant for Role 'B' users.
5. Some sample codes I should be able to allow view/download to Role 'A' users as well as Role 'B' users.

I am currently using the 'showdownload' module.

I have presently been able to accomplish the following.

I have created 2 roles A and B
I am able to restrict view/download access to certain sample codes to the 'authenticated user'.
However it is seen by both Role A and Role B users.
I have done this by coding it in the showdownload module

Any help ASAP would be appreciated.