Pretty neat competition, I think I picked a too easy to model building though, seeing as I finished in 90 minutes, modeling pretty slow and sitting around some of the time. Even my breakfast and coffe were included in that time, that's why the submission says ~80 min.
Anyhow, it's the Dome of the Rock. There's things and arches missing, but the tri-limit didn't allow me to go any further. The tricount is at 944 triangles.
Might give this a second try and go for a more complicated model
As for the workflow. I found a blueprint of it on google. Put it on a plane in max, modeled pieces of one wall section and simply rotated a copy of it 180*, then rotate that one 45* 3 times and the walls are pretty much done.
After that I just used some primitives and created the roof, nothing complicated there really, just extruding and optimizing all the way
/edit: forgot the photo:
Cheers!