Interested in building an earth home eh? Cool...and clearily you've done some homework on the subject, I've built two of em' in my younger years, ain't much to them really, alot depends on the amount of $$ that you want to sink into it, as materials vary, Our first one was built out of cinder blocks, coated the outside walls with plastic emulsion, [tar] and slapped 2 in. bead board on the walls and backfilled. Didn't put dirt on the roof though, R-Factor wise, I framed the roof on top and put in R-30 insulation, [equivilent to about 3 foot of earth I believe] Second earth home was a small two room one, took plywood and built half-wall forms with re-bar, then a wheelborrow run ramp with a small cement mixer.. only took a week to get all the footings & 10" walls pours, wife had the job of hammering on the walls filled with cement to compact it, but it was a hussle-hard working days until done... then tared the outside walls, put cross-ties as a solid slanted roof, covered also with tarpaper, tin and tar, and backfilled... the backhoe that backfilled it was sitting right on top of the roof... [strong enough to support a train actually..] Though I should have put 2" beadboard on the roof too, as twice a year when the wide temps swings, there was signs of condensation on the roof, so had to keep painting over the stains on the drywall... Straw bail houses are very simply and easy to build too, with a 60 R-Factor... It's the R factor that's reallly important, unless you're wanting a nuke shelter, and that can always be built into about kind of home structure. Hope this help.. God bless!