There are A frame houses, but the basic construct is just 2 walls connected at the top such that the walls are essentially the roof. You could think of it as a double lean to shelter.
Think of a swing set with no swings. Now throw a tarp over the whole thing and you have a big tent. Make the same thing from logs or lumber and close in the sides as you see fit. You can even use a tree as one side. This is no different than using a tarp to make an A frame tent - run a string between 2 trees, throw a tarp over it and stake the ends down. Shelter in 5 minutes.
Here is about as simple as you can get - make 2 big 8' triangles. Connect them at the top with an 8' long board, log, whatever. Now you have what looks like a big giant sawhorse. Put corrugated metal roof panels on each side from the top board to the ground. Use the same material and close in each end, put a hinge on one end so you have a door. Ugly, not insulated, should last at least a decade.