The following shows a C# example that returns a MultiPolygon object.
public static MultiPolygon buildMultiPolygon()
{
MultiPolygon multiPolygon = new MultiPolygon();
multiPolygon.srsName = "EPSG:4326";
Polygon[] polygon = new Polygon[2];
polygon[0] = buildPolygon();
polygon[1] = buildPolygon();
multiPolygon.Polygon = polygon;
return multiPolygon;
}