I know how scary it can look and be to do something like this BUT, its farely easy
Here is what I would do: I would make maybe a 12x16 or12x18 rectangle cake and cut into 4 pieces. I would also make a 12x12 square cake and cut that into a triangle, this will be the top of the house. Begin to stack the pieces like so:
cake/filling/cake/filling/cake board/cake/filling/cake/filling/cake board then add your sharpened dowels through all of them for extra support.
*Then stack your triangle roof and add supports as well. By this time you will know if you have enough support inside and I believe this is enough
Then you crumbcoat, let set and ice as usual.
I would cover it in 2 pieces (front and back) with the sides meeting directly on the sides of the house to look like a seam. Then continue to decorate to achieve the look you want.