On the original challenge
Debunkers have not fared well with challenegs offered by conspiracy theorists; there is a long history of challenges in the Flat Earth domain, some of which have been decided in court, and the answers to the challenge have never managed to convince the challenge setter. They're not a means of learning, they're a means of propaganda. So, realistically, I don't expect that Jim Hofmann's challenge can be met in a manner that Jim Hoffmann would concede to.
Therefore, it makes sense to consider the challenge as a starting point to making a household model that would demonstrate some principles of the WTC collapse to laypeople, even if it wouldn't serve to convince any truthers.
My own approach to that would be to utilize the domino effect, where a small lateral impulse can set dozens or hundreds of dominoes toppling.
1) I'd make a square floor plate, cut it in half, then set it on dominoes such that we have a square floor, but I can push the plates apart a little, and they will then continue to move apart as the dominoes holding them up topple over.
2) Obviously, stack several floors of these.
3) Make a hole in the center of the square = a semicircular hole in each rectangle. Make a heavy conical weight (maybe from cement) slightly larger than the hole, so that it can be dropped down the shaft of that multi-storey domino floor building. The cone, if dropped, would push the plates of the top floor apart (losing some energy), gain some energy dropping to the next floor, lose energy pushing these plates apart, etc. The weight of the cone and the distances need to be adjusted to make this process unstoppable.
4) It helps to make the "seam" rotate 90° from one floor to the next.
5) Wrap the whole structure in a paper shell; tack the paper to the floor plates. (Or use cling film?) This provides 100mph wind stability. Burn the shell away as the first stage of demolition. Put the cone weight on a paper support that also burns away after the paper shell has burned.
6) Instead of dominoes, use toothpicks to support the floors. This is aided by conical depressions in the floor boards, and two "comb" type supports that can be put at 90° , leaving holes to support the tooth picks until the next floor plate is placed that fixes the tooth picks in place; the combs can then be pulled out sideways. The picks would need to be set at a slight inward slant to keep the construction stable when the paper shell burns away.
7) Instead of 2 rectangles, 4 approximately triangular sections per floor.
The model would demonstrate a two-stage top-down collapse that is energized by a falling weight and enabled by the loss of lateral rigidity, with mass being propelled outward by the collapse.
The floor plates and combs would need to be created once through manual labor, or by CNC, or possibly by 3D printing, though that would not work well with the idea of burning away the paper shell. If the floorplates are made from metal, the paper shell could be held on by magnets.
P.S.: it occurs to me that the cone weight does not need a special support; it would simply sit in the hole of the top floor until the burning of the outer shell allows the plates of this floor to move apart. The process should then be mostly self-sustaining if the weight is heavy enough.
