PHP - Slider tipo catálogo para un echo

function ComprasWeb($sys)

  {

    $return = '';

    if($sys == 1)

    {

      $consultar = mysql_query("SELECT * FROM items ORDER BY ID ASC");

      while ($items = mysql_fetch_array($consultar, MYSQL_ASSOC)) {

      echo  '

            <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.0/jquery.min.js"></script>

            <form action="/tienda/comprar-items?id='.$items['ID'].'" method="post">

            <div class="col-lg-vehs">

              <div class="panel panel-default">

                  <div class="panel-body">

                    <div class="panel panel-default text-center">

                      <ul class="list-group">

                        <li class="list-group-item"><img src="/imagenes/items/'.$items['ID'].'.gif" class="img-thumbnailveh"</img></li>

                        <li class="list-group-item-vehs ContenidoTabla">ID: 123</li>

                        <li class="list-group-item-vehs ContenidoTabla">Item: Nombre</li>

                      </ul>

                    </div>

                    <center><input type="submit" id="BotonComprar" class="Boton" value="Comprar" ></center>

                    </div>

                  </div>

            </div>  

            </form>

            ';

      }

    }

<?php echo ComprasWeb(1); ?>