The following diagram shows the overall interior dimensions of the structure in scale feet.

There were two reasons for why I decided to create the interior floors. One was that I wanted to model some portion of the interior, and the other was that the structure's walls aren't straight. By bracing the interior with the first and second floors, the structure's walls will become straight.

The two interior floors were cut from gray Plastruct sheets and the roof was cut from 0.040" white styrene. All will be painted, so choice of material doesn't really matter.

I marked the sheets according to the dimensions shown in the diagram above, and then used the score-and-snap technique to break off the desired sections. I did have to do some minor filing to square up the cuts.