Makes a pie chart, regardless of input. You have to add this in the index page, though: <script type="text/javascript" src="http://mbostock.github.com/d3/d3.js?2.1.3"></script>.

pie-chart.html

<link rel="import" href="../bower_components/polymer/polymer.html">

<!--DONT FORGET THE ATTRIBUTES, YOU ATTRIBRUTE!-->
<polymer-element name="pie-chart" attributes="houseval flatval farmval">
    <style>
      .slice text {
        font-size: 16pt;
      }
    </style>
    
    <template>
      <span class="crust">
        <svg id="pie" hs="{{houseval}}" flt="{{flatval}}" frm="{{farmval}}">
          </svg> {{lastClose}}
      </span>
    </template>
    
    <script>
      function makePie(form) {
        var svg = d3.select(form);
        var w = 500,                            //width
            h = w,                              //height
            r = (w / 2),                        //radius
            color = d3.scale.ordinal().range(['rgb(216,179,101)','rgb(245,245,245)','rgb(90,180,172)']);

        var data = [{"label":"house", "value": svg.attr("hs")}, 
                    {"label":"flat", "value": svg.attr("flt")}, 
                    {"label":"farm", "value": svg.attr("frm")}];
        
        var vis = svg                       //we already have an svg element
            .data([data])                   //associate our data with the document
                .attr("width", w)           //set the width and height of our visualization (these will be attributes of the <svg> tag
                .attr("height", h)
            .append("svg:g")                //make a group to hold our pie chart
                .attr("transform", "translate(" + r + "," + r + ")");    //move the center of the pie chart from 0, 0 to radius, radius
     
        var arc = d3.svg.arc()              //this will create <path> elements for us using arc data
            .outerRadius(r);
     
        var pie = d3.layout.pie()           //this will create arc data for us given a list of values
            .value(function(d) { return d.value; });    //we must tell it out to access the value of each element in our data array
     
        var arcs = vis.selectAll("g.slice")     //this selects all <g> elements with class slice (there aren't any yet)
            .data(pie)                          //associate the generated pie data (an array of arcs, each having startAngle, endAngle and value properties) 
            .enter()                            //this will create <g> elements for every "extra" data element that should be associated with a selection. The result is creating a <g> for every object in the data array
                .append("svg:g")                //create a group to hold each slice (we will have a <path> and a <text> element associated with each slice)
                    .attr("class", "slice");    //allow us to style things in the slices (like text)
     
            arcs.append("svg:path")
                    .attr("fill", function(d, i) { return color(i); } ) //set the color for each slice to be chosen from the color function defined above
                    .attr("d", arc);                                    //this creates the actual SVG path using the associated data (pie) with the arc drawing function
     
            arcs.append("svg:text")                                     //add a label to each slice
                    .attr("transform", function(d) {                    //set the label's origin to the center of the arc
                    //we have to make sure to set these before calling arc.centroid
                    d.innerRadius = 0;
                    d.outerRadius = r;
                    return "translate(" + arc.centroid(d) + ")";        //this gives us a pair of coordinates like [50, 50]
                })
                .attr("text-anchor", "middle")                          //center the text on it's origin
                .text(function(d, i) { return data[i].label; });        //get the label from our original data array
        };

      Polymer('pie-chart', {
        ready: function() {
            makePie(this.$.pie);
          }
        });
  </script>
</polymer-element>