More sketches than drawing but they provide an idea of the construction method.
Each floor is independently supported with its own posts from the ground floor – see posts in grey for first floor and yellow for second floor (further down the page).
Going with the naming convention of ground floor, first floor then second floor (making three levels).
Each row of posts level is connected using the floor joists and cross beams.
Posts to support second floor from the ground up added into structure.
The ridge pole is independently supported by 5 king posts from the ground floor.
The rafters are bolted above the ridge pole and also nailed where they meet the edge of the second floor. This forms a (self supporting) triangle so in theory the ridge pole could be removed once the rafters (nungo) and horizontal mbariro are secured.
Braces were added between each upright and cross beam at each level (not shown in these drawings)
The structure is now self supporting as the pictures up the point of the roof going on show.