The his website is about the relationship of geometry and architecture specifically measurements. In the 8th slide it talks about how architects use geometry by knowing the angles of the corners in order to build it. It also talks about how architects must use the Pythagorean theorem for measurements of buildings as well. These are some ways architects use Geometry according to this website though theirs a lot more.

https://prezi.com/vbx3e1y66dal/how-architects-use-geometry/

some links:

http://www.ask.com/art-literature/architects-use-pythagorean-theorem-3b4d76cf78a33207#full-answer – the Pythagorean theorem and architecture

https://sites.google.com/site/geometrytheorems/geometry-in-reality/geometry-in-architecture geometry and architecture