Building a micro house/ TINY house

So, ive always been interested in alternative living. I've allways wanted to be rather free, no ties holding me down, being free to leave for a few moths when i feel like it. Recently ive been looking at these 'microhouses', there just what it sounds like, TINY houses, ussualy one room.

i was wondering how much you think it would cost to hire someone to build one. this is what i was imagining

2 story, but the one would just be in a massive hole in the ground.
so, bottom floor would be:

saay 4mX3m,
about 2.5m high
very basic, just walls (brick im guessing)

and then the floor above would be:
a 2mX3m (just enough for a bed, dresser & drawers) and out 2.5m high
1 window, with a fly screen

and then a little porch outside, say
2mX3m (enough room for just chillin n a table or sumin)

how much do you think it would cost to hire a conracter to make it? would it be a hard project to build one my own (with the help of some freinds)?
Would it be made out of brick or wooden?