Suggestion:
System has the provision where the users can set the users site rights. This is defined for users to have assess for the particular site. Users site rights menu is available in System-> System Setup->Masters-> User Site Rights. This is applicable for “Normal” type users.
The User has to enter or select the user id for which he has to give the rights, Select the site for which the rights are required and select all or selected particular profiles to save the record.
Please note: If the user is 2 level then single site wise rights can be assigned, if the user is 1 level all sites but limited menus rights are assigned, And 0 level user can have rights for all sites.