3D - Underside of a pointed angular structure

Greetings, any idea of how to create the angles under the roof of an angled, pointed wing of a building? It's like the prow of a ship. Is it possible to create an upside-down skillion under the roof? Image here: https://commons.wikimedia.org/wiki/File:Denver_Art_Museum_2.jpg

The pointed portion will not touch the building underneath: https://www.openstreetmap.org/edit#map=20/39.73690/-104.98911

Feel free to tell me how or to do the work yourself, if you've got the mad skills ;)