i was looking at domes a while ago. here's a guy who built one underground in montana....didn't need heat or air conditioning. the house was insulated under an umbrella of insulation and polyethylene.
http://www.axwoodfarm.com/PAHS/UmbrellaHouse.html
here's a guy who sewed his own airforms and inflated them with multiple bathroom ventilation fans.
http://www.geocities.com/flyingconcrete/lloyd-turner.htm
here's a cheap method of building an underground monolithic dome:
dig a hole big enough for the dome footprint (it has to be deep enough for a concrete truck to pour on it later). bend a pipe to a shallow angle, cover the body in concrete (except for the ends) and push rebar through it. it will bend the rebar to a consistent angle throughout. these are your vertical pieces that you will stand up in a circle, converging at the top of the dome. then, wrap rebar around the outside of this dome frame. now you have your frame. backup a concrete truck and pour several inches on top of the frame (don't back it up too far, or you'd have to make the soil is up for it). once its cured, just lay a sandwich of plastic/insulation/plastic above the dome for insulation. domes can be buried underground because of their compressive strength.
there's some confusion here and there about where the insulation should be. i advise putting it on the outside of the concrete so your concrete is thermal mass, stabilizing temperatures better. i've read some stories where people put sprayed foam insulation (which is high quality stuff) on the inside of their domes. with climate control, its very easy to maintain a temperature, but the moment someone uses the oven, they're turning up the AC and opening the windows in the kitchen. no good.
one problem people have with insulation on the outside of the concrete is water vapor getting in the foam between the concrete and the dome cover. if you're underground and your foam is covered with a plastic umbrella, no worries. if you're above ground, get some grancrete to seal the insulation. it must be completely sealed, or else the insulation could get soggy and stop working.
