The following comment comes from Earth-Sheltered Houses by Rob Roy (who also expands on this subject in his brilliant book Mortgage Free).
More than a third of the average American’s after-tax income is devoted to shelter, usually rent or mortgage payments. If a person works from age 20 to age 65, it can be fairly argued that he or she has put in 15 years (20 in California) just to keep a roof over their head. With a piece of land, six months’ work, and — say — $35,000, he (or she) and his family could have built his own home.
To save 14½ years of work, you cannot afford not to build, even if it means losing a job while you do it. Granted, the land (and the $35,000) has to come from somewhere, but this amount is no more (and probably no less) than the down payment on a mortgaged contractor-built home, and about half the cost of a new double-wide mobile home (figuring either option as being about the same square footage as an earth-sheltered home).
And what do you get for your time and money? You get a comfortable, long-lasting, energy-efficient, environmentally compatible, low-maintenance home. You get the design features that suit you, so that the house fits like an old slipper. You get built-in fire, earthquake, and tornado insurance. You get intimite knowledge of the home so that when maintenance or repairs are required, you’re the one best placed to make them. You get tremendous personal satisfaction. And you get freedom from a lifetime of economic servitude.
Rob Roy actually sits on the “expensive” side of DIY underground construction — earthships and various other super-cheap underground homes are well below his $35k estimate and certainly well below the cost of, say, a new car. Couple that with inexpensive land from a company like Dignam Land (in Canada), or various other companies around the world selling rural land from tax sales, logging properties, and so on, and the whole project can be done for less than the down payment on any home would be…
So… why don’t more people do it? Is it really worth giving up 15+ years of your life (and I’d say for many people, more) to pay off the house you live in just to save yourself the effort of having to do it yourself?

Surely it can’t be that a life of 9-to-5 indentured servitude is so wonderful that one can’t give up a summer or three building a house like the one above, which I believe came in at about $20,000… And with an increasing percentage of people defaulting on their mortgages and losing all of those years, even on a risk management level it seems completely nonsensical.