Planning cob building for later addition

I'm reading books on cob building and am planning to build a small house. My plan is for a house with a rock stem wall foundation, an oval shape, and a simple gable roof with two sides. There will be one round center beam (tree trunk) spanning the building. The center beam will support dimensional lumber beams, on top of which there will be dimensional lumber boards. Large plastic laminate roofing pieces will cover the boards. I chose this type of roof because I am a novice builder and where I live roofs are commonly built like this. I currently live in an adobe house with this exact type of roof, and I think it's something that I can imitate myself on a smaller scale, designing the size and dimensions of the new cob building to coincide with the size of the straight trees on my property.

The way these types of roofs are built here, the center beam sticks out into the open air on the outside of the house, with the roof covering the beam. Since the beam ends are exposed, sometimes people put buckets on the ends as a way to try to further preserve them. Most of the year is dry, but it rains heavily for five months a year (around 1000 mm).

My plan is to build one small room (maximum 20 m2) with this style of roof and later add a series of other similarly-sized rooms, creating a chain of rooms linked together. I have plenty of space to build in this stretched-out style, and I want to keep the rooms one-story to allow for easier building. Building like this will also allow the building to have a long stretch of southern wall, helping to keep it warm.

(In this coldest months, it gets down to below 4 C at night and up to 20 C in the day (38 F to 68 F), with very strong sun due to the location and moderately-high elevation (2200 M).  I've lived in very cold adobe houses here that didn't get much sun due their proximity to trees, but a thermal mass style house, if positioned correctly, can be very comfortable due to the strong sun and relatively high daytime temperatures.)

With hired help to allow for faster cob mixing, I think I can reasonably expect to get one of these small 20 m2 rooms finished myself during a dry season. Then I can wait and continue building my little rooms in a row in the following dry seasons.

My questions is about how to connect these small rooms. My original idea was to have a series of these small rooms and then not even link them up at all, since the climate allows for this. My next idea was to link them up with covered walkways, or maybe cob hallways with their own independent roofs. Gutters are used here to collect rainwater, which helps immensely with the roof runoff during the rainy season.

Then I realized that these plans would necessitate building an extra wall. If I could link up the rooms in a smarter way, I'd only have to build 3 walls instead of 4 for the second room. What I'm having trouble visualizing is how the roofs would connect. My biggest question is: where would I place the tree trunk center beam in the second room? What would support it?

As I'm sure you can tell, I know very little about building and nothing about architecture. Would anyone be able to point me in the direction of some resources that might answer my questions?

Thanks for reading, Saludos

One question that might help suggest an answer is, is there a slope from side to side in the area you want to build these rooms? If you make the first one, then the next and the next a step up or down, you could make the roofs nest over or under their neighbors, and potentially allow a pocket in the first wall for the beam of the next to slide into.

Thanks for your reply. The building site has a slope that runs down towards the south south-west. The eventual long building would run more or less from east to west. So I don't think I'd be able to take advantage of that slope.

From what I gather, the second room/building is always going to have to have four complete walls, rather than three, and then the idea is to have its roof a little lower or higher than the roof of the first building?

The adobe building i live in has a loft on one side, over the kitchen, and so the couch and desk are in an area with a high roof, which I found I really don't like-- another reason I wanted to make one story rooms with fairly low roofs.

Also, I'm open to other roof styles. It just has to be something relatively easy to construct and also easy to attach gutters to, since the only source of water on the property is rainwater. A friend in the area made a reciprocal roof that's very impressive visually, but I'm not sure I want to deal with the complications it seems to present at the time of building.

I hope this photo can give a better idea of the type of roof I'm planning. My building would be similar but made of cob, and without the steel/concrete beams and posts, and also much lower.