Check out switch_xml.c. I think a good example of this might be "fifo list_verbose". In mod_fifo.c approx line # 3644 it creates a new object of type switch_xml_t using switch_xml_new(). I think you'll find some handy things like adding xml child nodes, etc. Look in mod_fifo.c at the function list_node() for an example of how you can use the included tools to build up an XML structure. Then you can convert to text with switch_xml_toxml() function. Search for this line in mod_fifo.c:
xml_text = switch_xml_toxml(x_report, SWITCH_FALSE);
The context around that line is a good example of using these objects, printing them out and then safely freeing them from memory.
-MC