Construction

Why Torus: A torus might be a better shape for a homemade shelter than a dome. While a large concrete dome with a steel framework might be nice, it might be hard to make also.
How to make: A torus has most of the strength of a dome, but with more flexible contrsuction possibilities. A couple of ideas:

Using 4 huge concrete or metal 'elbows', bolt together a torus. Water seal the whole thing somehow. Probably very expensive, and heavy.

Loop together 8 steel pipes with heavy rope or cable into a circle. Make 16 total. This forms the longitude. For the latitude, make 8 more circles in the correct sizes needed. The following picture shows the longitude in blue, and the latitude in red

It would be best to figure out all the exact lengths of pipe needed beforehand. I'll come up with some measurements soon. Now you have 24 circles total. All you have to do now is tie them all together tightly, probably with big wraps of binding wire at each vertex.

Waterproofing: Once the framework is done, take some cellophane wrap (heavy kind, skid-wrap. Kitchen cellophane would work but you'll need a lot more. Skid-wrap comes in large rolls, used in factories etc.) Wrap it around the torus framework as much as you can. Use a lot and wrap it up tight. Wrap vertically, as shown in this picture. Many cellophane layers should provide very nice insulation properties, as there will be a small layer of air between each layer of cellophane. This should waterproof it pretty good, except for one problem.

The Door: The door presents a significant problem, because all your waterproofing efforts are nil without a waterproof door. There's not easy answer, but I would only use one 'facet' of the torus as the door, so you don't break the framework. The door should probably be a large screw-on cap or something, so it won't leak as much. Placing the door on the side might be a good idea too.
Finishing: A cellophane-covered torus obviously won't cut it--it must be covered with something tough. You could cover the whole thing with dirt, or dump concrete over the whole thing. If using concrete you should make a circular pool of concrete on the ground as big as the torus, then set the torus in it. Then pour concrete over the top. That way all sides of the torus are coated, including the bottom. Make sure there's no holes in your cellophane, but if you wrapped enough it should be *hard* to poke holes in it. If covering with dirt, you'd better wrap it with something else after using *lots* of cellophane. You really need to coat it with something hard like concrete so animals don't burrow in. You might want air circulation so you don't suffocate, have fun figuring out that one.
Other Possible Benefits: If the middle is left hollow, you could climb on top the the torus, and throw flammables in it. You could heat the shelter from the inside-out this way without smoking everyone out. Maybe put a smoke-flap on top so the rain don't snuff out your fire. People could have a little more privacy in a torus, since one side is hidden from the other. You can expand a torus, just by adding more toruses around it. Or design it like that in the first place. You can build one around a lone tree so it don't go nowhere.

Offered by Joe.

PS: I tried to be clear in the descriptions, if not don't hesitate to ask. I'll be working on models, so please offer suggestions, even if they sound stupid. Stupid ideas are usually the best ones. And no, spraying styrofoam or InstaPak on the outside isn't a stupid idea. Neither is the pink-panther insulation stuff, you can sandwich that between 2 layers of heavy cellophane before concreting. Anything goes.