Create permissions to a SharePoint list using Object Model

SPSecurity.RunWithElevatedPrivileges(delegate()

{

   using (SPSite spSite = new SPSite(siteUrl))

   {

      using (SPWeb spWeb = spSite.OpenWeb())

      {

        if (spList != null)

        {

                               

           spList.BreakRoleInheritance(true);

           SPRoleAssignment roleAssignmentAdmin = null;

           SPRoleAssignmentCollection SPRoleAssColn = spList.RoleAssignments;

           for (int i = SPRoleAssColn.Count - 1; i >= 0; i--)

           {

               SPRoleAssColn.Remove(i);

           }

     //ProjectWorkspace Owners

  SPGroup grp_PWOwners = spSite.RootWeb.SiteGroups[Constants.GrpProjectWorkspaceOwners];//ProjectWorkspace Owners

  roleDefinitionAdmin = spWeb.RoleDefinitions.GetByType(SPRoleType.Contributor);

  roleAssignmentAdmin = new SPRoleAssignment(grp_PWOwners);

                                       roleAssignmentAdmin.RoleDefinitionBindings.Add(roleDefinitionAdmin);

                                spList.RoleAssignments.Add(roleAssignmentAdmin);

//Workspace Administrator

grp_PWOwners = spSite.RootWeb.SiteGroups[Constants.GrpWorkspaceAdministrators];//Workspace Administrator

roleDefinitionAdmin = spWeb.RoleDefinitions.GetByType(SPRoleType.Administrator);

roleAssignmentAdmin = new SPRoleAssignment(grp_PWOwners);

                                roleAssignmentAdmin.RoleDefinitionBindings.Add(roleDefinitionAdmin);

spList.RoleAssignments.Add(roleAssignmentAdmin);

//Workspace Administrator

grp_PWOwners = spSite.RootWeb.SiteGroups[Constants.GrpReaders];//Workspace Administrator

roleDefinitionAdmin = spWeb.RoleDefinitions.GetByType(SPRoleType.Reader);

roleAssignmentAdmin = new SPRoleAssignment(grp_PWOwners);

                                roleAssignmentAdmin.RoleDefinitionBindings.Add(roleDefinitionAdmin);

                                spList.RoleAssignments.Add(roleAssignmentAdmin);

spList.Update();

                                                            }

          }

      }

 });