Excerpt from a CityGML file containing one building modelled as a <gml:MultiSurface>

citygml_multisurface.xml

<?xml version="1.0" encoding="utf-8"?>
<CityModel ... >
  <cityObjectMember>
    <bldg:Building>
      <bldg:lod1MultiSurface>
        <gml:MultiSurface>
          <gml:surfaceMember>
            <gml:Polygon>
              <gml:exterior>
                <gml:LinearRing>
                  <gml:pos>0.8 0.2 0.2</gml:pos>
                  <gml:pos>0.9 0.3 0.2</gml:pos>
                  <gml:pos>0.5 0.5 0.2</gml:pos>
                  <gml:pos>0.8 0.2 0.2</gml:pos>
                </gml:LinearRing>
              </gml:exterior>
            </gml:Polygon>
          </gml:surfaceMember>
          <gml:surfaceMember>
            ...
          </gml:surfaceMember>
            ...
        </gml:MultiSurface>
      </bldg:lod1MultiSurface>
    </bldg:Building>
  </cityObjectMember>
</CityModel>