Easy to produce, easy to setup, self supported, but limited modularity.
Drawing 1A
Drawing 1B
Photo 1C
Photo 1D
This is probably the easiest, and the best looking system. The basic piece is simply 1 module that could be put side by side and over existing DF or MBS setups. The sides of basic piece is filled, (not hollow) so they can be used alone, or in combination with the edge pieces. Two edge pieces could also be put together to form the top of a tower or narrow building.
The only drawback is that the width is fixed. So you would need to make 4, 6 and 8 inches wide modules. I don't think much people would make buildings with roof, larger than 8 inches.
The 2 additional pieces would greatly enhance the look and fonctionnality. The one with the windows is simple (photo 1C) as it is basically the same as the basic module, plus the windows. The other one can be used to have a roof that connect over another roof at 90 degree (like the photo 1D). You have to decide if you want to have the same angle on all roof modules, so it will work against any other roof. Having the same angle mean different heights. If not, it will only work on modules with corresponding slope. It could also be used alone to have a pointy roof that goes over which is a nice variant.(excuse me if it is not very clear, but english is my second language) I hope the drawings will speak for themselves.
In short, this would make between 2 and 4 modules for each width you choose to produce. The modules could probaly not be molded in 1 piece, but probably in 2 pieces, then glued together.
I'm sure you can come up with a tile pattern that would make the joints seamless.
Optionnal: make half modules (only one slope) to allow more complex roof systems
In my opinion, this one would be the best, even with the width limitation. It is quick and easy to setup and self supported.
UPDATE:
Here are the first prototypes for the first system, they are reversible, meaning that one side is MBS, and the other side is stone
The second module is a windows, and also an intersection to other roof sections
The chimney is a kind of hook to support the window module.
Note: I think the angle of the slope is too steep. It was easier to make this way because it was a 90 degree angle. If I want the modules to be compatible, the slope as to stay the same for all, but longer modules (I plan up to 8 inches) will be way too high. Maybe i'll scrap everything and start over with a wider angle. These are PROTOTYPES, They are for testing purposes. The final version will be more accurate and detailled.
This is the one I submittted in 2003. More small modules, need interlocking system for the sides, need support from underneath, but very modular.
Drawing 2A
Drawing 2B
This setup would allow every combination of size, but is more complicated to setup. And without an interlocking system, the pieces will move too easily.
As for the needed support, back in 2003, the proposed support were interlocking beams grid, but it was too complicated. But the same system that is used for the roof on the first system could be used to make the floor supports. Using a few 2x4, 2x6 and 2x8 inches boards (1/4 inch thin) could make all the support we would need for the floors. They should have a wood plank texture. It would even allow half floors, where only part of the building has a second floor, without needing support from pillars.
Maybe you can work on this one and try to make it better. Anyway, I'm sure you are already working on a system that would allow to "pile-up" modules, since it would be needed for any larger standing structures (building, castles) Ever tried magnets ? Maybe a totally different system with larger pieces and less modular would be needed for larger buildings anyway. We can't possibly make a Castle with the current modules. It requires a different system, as long as it could be matched with DF modules when needed.
Contact me if you have any questions