I like the concept, I do.  It really needs about another 2,000 square foot thoubh before you can: watch the games comfortably, entertain with parties, have relatives come to visit, and not get laughed at the by most ladies one would like to bed.

I want one…

£3000?!! I’d have one if it weren’t for buying the land and planning permission

Not really so much in house buying terms

An understatement. The cheapest bedsits around here cost around £60000ish, average house price around £180000ish

I like the idea of living in nature, I would like to try being homeless at one point just to see what it’s like even if I do own a flat by that time, and in woodland you’d be safer, sheltered a little from rain by the trees and might be able to forage for berries, as long as you stay alive you won’t need to work and escape all other pressures of society. It’s also comforting to know that if I lost my job and became homeless I could do that

I love that. It’s right up my alley.
I considered this concept about 20 years ago but I wanted much more light than I thought a hovel could deliver.
Looking at this though, I see there could have been plenty and it would have been much cheaper to build than what I eventually did build ... The Pyramid.
Les, I’ve figured I can put together my own post about that so delete it from the bottom of your to do list ... if you haven’t already. 
Consi, you miss the point of the concept which has more to do with living alone in one’s own, very cheap to produce space, with no fear let alone care of others’ judgement.
Let’s face it; if you care Where you’re fucking you’re not fucking, you’re doing peacock stuff and if the woman cares she’s just too damn shallow to care about.
Then again, if you provide enough strategically placed mirrors round the fucking place even a shallow woman could be happy.
It probably says a lot about the women I’ve ‘known’ but I can’t think of one who wouldn’t have wanted to fuck in a place like that at least once but   none would have wanted to live in it permanently, even with me, even when I was young and beautiful.

if the woman cares she’s just too damn shallow to care about.

Who said anything about caring?  Sheesh!  I was just talking about bedding a gal.

Gals were always easy. I was talking about women.

Two things I’d worry about as I went about building one of these: ventilation and mold.

And, well, 1,000-pound horses walking over my bedroom in the early morning, as they grazed the roof.

And, well, 1,000-pound horses walking over my bedroom in the early morning, as they grazed the roof.

And cattle. That is a valid point I hadn’t considered.

Considering the tiny footprint of the house, couldn’t you just fence off the roof to keep your bovines and equines from falling through?

Many buttercups are poisonous to grazing animals

from http://www.mchenry.edu/Faculty/mgarriso/FieldGuideToMcHenryCounty/MCCDWildflowerGallery/SpringWildflowerGalleries/SpringWildflowerYellowOrangeGallery/pages/ButtercupBulbous.htm

But i’m not sure if planting them will actually discourage them, give evolution some more time maybe and either all the buttercup eaters get phased out or all cows gain the ability to digest them

Reminds me of the ‘town’ of Coober Pedy in South of Central Oz.
Here are some examples of underground living.
Here are a couple more.