The 16' square room on the left was the original structure. It stood alone for a mere 8 months, before the planned addition to the east was put up. Why did we do it like that? Well, inexperience was the #1 reason. I had no idea what it would involve to singlehanded build a cabin, so going as small as possible seemed crucial. Also, we had some time constraints involving an out of state summer job, and the need for shelter when returning. Would I do it in stages again? Absolutely not! Preserving structural integrity and weather tightness with this sort of add-on has been challenging beyond reason. And the overall looks suffer too.
That said, the seemingly crowded and complicated layout of the east addition works super well in reality. Our bedroom is the best place in the house. The covered entrance and mudroom is well proportioned and does the job of filtering out cold air, snow and dirt from the living module. The guest bedroom is mostly a well organized gear cache containing all we need to backpack and rock climb, plus a work bench. In a matter of minutes it can all be stuffed in a duffle and replaced with a mattress, a couple of houseplants and some magazines, preparing the room for overnight guest(s).
And the bathroom? I guess we humans feel weird without one nearby. Personally I rarely set foot in there, preferring the fresh air of the outhouse for that business, and also exclusively use the outdoor solar shower when in season.
The loft is only over the left hand 16X16 section, and effectively one rather sizeable room, if you disregard the fact that adequate headroom exists only right under the peak...