Your have two options, you can create a collada model of the air space, or a series of polygon objects defining each face,
verticly oriented polygons can be defined, be take note of the direction of your (clockwise or counter clockwise) as this will effect the style, viewing a polygon from the bottom makes it slightly darker
for a simple rectancular shape you will need 6 faces
the following kml is a modified version of the pentagon example with one of the verticle faces filled in, the other 4 verticle faces need to be complete, but you'll get the idea.
<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2" xmlns:kml="http://www.opengis.net/kml/2.2" xmlns:atom="http://www.w3.org/2005/Atom">
<Document>
<name>pm1.kml</name>
<Style id="poly">
<LineStyle>
<color>f0ffed42</color>
</LineStyle>
<PolyStyle>
<color>e8ff9257</color>
</PolyStyle>
</Style>
<Placemark>
<styleUrl>#poly</styleUrl>
<Polygon>
<altitudeMode>relativeToGround</altitudeMode>
<outerBoundaryIs>
<LinearRing>
<coordinates>
-77.05844056290393,38.86996206506943,500 -77.05552622493516,38.868757801256,500
-77.05315536854791,38.87053267794386,500 -77.05465973756702,38.87291016281703,500 -77.05788457660967,38.87253259892824,500 -77.05844056290393,38.86996206506943,500 </coordinates>
</LinearRing>
</outerBoundaryIs>
</Polygon>
</Placemark>
<Placemark>
<styleUrl>#poly</styleUrl>
<Polygon>
<altitudeMode>relativeToGround</altitudeMode>
<outerBoundaryIs>
<LinearRing>
<coordinates>
-77.05844056290393,38.86996206506943,400 -77.05552622493516,38.868757801256,400
-77.05315536854791,38.87053267794386,400 -77.05465973756702,38.87291016281703,400 -77.05788457660967,38.87253259892824,400 -77.05844056290393,38.86996206506943,400 </coordinates>
</LinearRing>
</outerBoundaryIs>
</Polygon>
</Placemark>
<Placemark>
<styleUrl>#poly</styleUrl>
<Polygon>
<altitudeMode>relativeToGround</altitudeMode>
<outerBoundaryIs>
<LinearRing>
<coordinates>
-77.05844056290393,38.86996206506943,500 -77.05844056290393,38.86996206506943,400 -77.05552622493516,38.868757801256,400 -77.05552622493516,38.868757801256,500 -77.05844056290393,38.86996206506943,500
</coordinates>
</LinearRing>
</outerBoundaryIs>
</Polygon>
</Placemark>
</Document>
</kml>