Ana54 wrote:
4. We build a small building to start with, adding on rooms and floors as our group gets bigger and as we get richer.
We can have a flat roof with stairs leading up to a door to it so that we can easily turn it into an upper floor, and then have stairs leading from that floor to the roof in the same way, so that another floor can be built over that one if we need to, etc.
Make sure to be careful with flat roofs. They're easier to build although they tend to be more challenging to maintain, owing to greater accumulation of snow and pooling of water putting more pressure unevenly across the roof and causing the occasional leak. (The reason you don't see as many of them.) Although if the intent is to make it sturdy enough to also be a floor at a later date, I believe that will change the construction somewhat.
Oh you might also consider looking into cob construction (although I don't think it works for multi-story buildings) because I believe they can be built fairly quickly, I know they're "dirt cheap" and I believe they can be set up with plumbing and electric (and of course phone & internet). Though as with anything I imagine there's a fair amount of research involved.