When you submit a list, the information that is sent is the value of the option. In your list, most of the options have the value attribute set to value:
<select class="formListfield_Large" name="fieldset_group_Type_of_roof" id="fieldset_group_Type_of_roof" tabindex="5" multiple="multiple">
<option value="">Select type of roof</option>
<option value="Polyurethane Foam roof">Built up roof</option>
<option value="Value">Modified Bitumen</option>
<option value="Value">Single ply</option>
<option value="Value">Tile</option>
<option value="Value">Shingles</option>
<option value="Value">Polyurethane</option>
<option value="Value">Foam</option>
<option value="Value">Other</option>
</select>
Take a look at the Single Ply Option:
<option value="Value">Single ply</option>
Since the value attribute is set to "Value", that is what is sent. If you want to send "Single Ply" when this is selected, you will need to set the value attribute accordingly:
<option value="Single Ply">Single ply</option>