1. First, create a custom permission level at the site Collection level. (Site
Settings, Advanced Permissions, Settings, Permission Levels, Add Permission
Level)
1a. If you do not see the Settings option on the tool bar, then the site is
inheriting from an ancestor. Choose Actions, Edit Permissions. Then repeat step
1
2. Choose the desired Base Permissions.
3. Click Site Settings, Advanced Permissions
4. Click on the [Site] Owners group. Clear the Full Control box and check Read
5. Click on the [Site] Members group. Clear the Contribute box and choose the
level created in step 1.