"big enough to accommodate a bedroom, lounge area and storage space"... .. no toilet? Not quite sure this is going to be a big seller.

That slanted window is wasting a lot of space.

And let us remind ourselves that weather in Finland is not that predictable or dry on the best times and rather cold most of the time. The lack of lavatory you can always build an outhouse (and with this size "house" I think it is for the best.).

"while the retreat itself is a 50 sq ft "
5'x10" is 50' square. It's obviously wider then 5' so more like 7'x7'. Are they micro couches? Something is off in the translation from meters to feet I think.
I once thought of a building of that size as in Californian you are allowed a shed of 100'square. The maximum size vs cost I came up with, was a stretched (tall) geodesic dome as the sides can bulge out for extra elbow room and shelf space. But with that there was no room for a bathroom/shower area, that would have to be separate or a outside shower.

Is it so hard to get a building permit in Finland?
@telocity: "50 sq ft" and "50 ft square" do not mean the same thing. "50 ft square" means a square, 50 feet on each side.

I would have it slightly big enough for a bathroom. I would not mind having an external shower type fixture. It would make an excellent place to get away from things. :)

Looking at the photo 5 in particular gives you a good idea of the dimensions, because you can see a door which is about 1m wide (looks like a standard width door).
So, on that side it is about 3m wide, and 5m long on the longer side. That gives you 15m2 (50 sq. feet).

That would be roughly 160 sqft if your footprint calc of 3m by 5m is correct.

umm, does it have a microwave? You are not gonna poop if you don't eat

We have become to big for our own good, I would love a small home. . We really need to change the way we live, we have taken too much already, from nature. Its time to give back, reduce our impact on the planet. Light weight aerodynamic commuter vehicles, which are fun and good for the planet. Our lives and the things we use are all designed around energy use, large square boxes, weighing 2 tons to move one person down the road. A 2000 square foot home with little to no insulation, or other energy saving devices, materials using thousands of dollars to heat, cool, cook, remove waste, clean ourselves etc. Change can be hard, but the rewards, are a better, happier life, with a huge reduction in stress. Its not for everyone, but its the right thing to do if you care about the future and world your family will have to endure and live in. How do we start, education ?