Rebars

Now, beginning 18" to 24" off the slab level, you will run rebars horizontally around the circumference of the dome at that level. Begin by tying an end with wire (And/or welding) and work the rebar clockwise around the circle until you return to the beginning. Do the same every 18" to 24" up the dome until you reach the top. At this point, you will have a better idea of the shape of the dome.

Take the remaining four rebars (two on each side of the door) and bend them in a smaller arch, crossing them over each other at the top, in front of, and just above your desired door height. This is hard to visualize, except to say you will create a skeleton/frame for an arch in front of the door similar to the arch over an igloo door. Looking down from the top, you will see two "x's", one in front of the other, that frame-out the arch. Stick the ends of the rebar in the ground (Ideally, you can pour a separate, smaller footing). Use one horizontal run, at least, in connecting the door-arch with the dome horizontals.

I know this is somewhat vague without a drawing, but the general idea, here, is to create an arch over the door for protection from rain. The door should be low, requiring a human to bow somewhat in order to enter. (Smaller doors are safer and promote greater structural integrity.) Wire all connection points where rebars cross (or weld).