It's not as detailed as Conan. There are no NPCs in your build.

Take a look at the screenshots to see what other people have built. There is wood and stone, and later on fancy wood pieces, glass cubes and roof shingles. There are also natural and crafted objects that glow, and some decorative items and furniture. The game has smoke mechanics so you have to make a workable chimney, and it has rudimentary load-bearing physics. You will need extra support beams, but natural rocks and building around trees (tree houses) can give you more height.

If you're into that, there are mods that give more building options.

Edit: I should add that limited terraforming is available, raising and lowering land, but you can't dig tunnels.