As far as the seats appearance, you'll need to use CSS to define a "container" of where you will store the seats themselves that has an explicit width, which you can see in the CSS my example provided : 

<style type="text/css">
        /* Defines your container width */
        #SeatingSection { width: 150px; }

        /* A generic class for each of your "seats" that specifies a size and will make them "float" */
        .seat { float : left; height: 20px; width: 20px; background : #ddd; margin: 2px; color: #fff }

        /* Coloring based on availability */
        .seat.available { background: green; cursor: pointer; }
        .seat.not-available { background: red; }
</style>

You could possibly use jQuery to add your "selectable" functionality so when an available seat was clicked on it would add a "selected" class to them and when your button was clicked, you could use the selected class to determine which seats were selected : 

<script type='text/javascript'>
    $(function(){
      //When an available seat is clicked on
      $('.seat.available').click(function(){
          //Toggle selection for this seat
          $(this).toggleClass('selected');
      });
      
      //When your "Purchase" button is clicked
      $("#Purchase").click(function(){
          //Grab the selected seats
          var selected = $(".seat.selected");
        
          if(selected.length == 0){
              alert("No seats were selected."); 
          }
          else{
              alert(selected.length + ' seats were selected. Proceed to Purchase screen.');

              //You may want to add some additional properties to store your seat ID within your
              //seat <div> elements so that you can read them here (look into HTML5 data-attributes)
          }
      });
    });
</script>

• Working Example

As far as actually mapping the values, you may want to create a numbering system that would output them in order (this part is a bit tricky) and may require you to sort them in a specific way to get them to output properly (especially if the venue doesn't have a very rectangular seating arrangement).