Building a model of a poured concrete building.

I want to build a small scale (8ft x 18ft x 10ft) model of a brutalist style poured concrete building. It will be a temporary structure, and I need to build it out of a material that can be broken down and removed quickly. I want it to mimic the seamless structure of the actual building, so a poured material would be better. Matching the main features and general feel of the building is more important that minute details. Any suggestions?

Here is the building:

Well I noticed that the symmetry of the building repeats itself. You could easily sculpt one form and mold it. Then create as many casts as you need in a foam product. Then you would only need to mold and cast the odd shapes. But do some research. This site will have everything you need: http://www.smooth-on.com/

Best thing I could come up with is this.

https://www.youtube.com/watch?v=cnQ_9E3DSjk