Begin by digging a round trench (12" to 18" wide) for the footing, using building codes applicable to the area. Be careful not to displace the perimeter stakes. (Note: Consider the possible climate change that would require deeper, below-freeze-level footings. Frozen soil heaves shallow footings.) Place horizontal rebar (perhaps ½" diameter, inner and outer ring) around the circumference of trench, inside, and heavy hardware cloth (4" to 6 " steel mesh) across the dome floor area. It is a good idea to first put a layer of sand, followed by plastic vapor-barrier under the hardware cloth. The forms, following the outer circumference of the trench should be installed (minimum 4". Pref. 6" high) for a monolithic slab that will encompass both the footing area and slab/floor area.
This concrete form can be done by attaching (tack and glue) long strips of layered ¼" inch exterior plywood (double or triple-band) to the inside of the large number of stakes around the outer circumference of the trench, at the same desired height above ground, making sure everything is level. The narrow (4" or 6" wide) strips will bend around the circumference of the stake circle. When you are done, you will have a plywood band circle around the outer rim of the footing trench, reinforced and secured to the inside of the perimeter stakes. It is a good idea, at this point, to "backfill" and pack soil around the outer rim of the band-form, as concrete is very heavy! Use water, if possible, to pack the soil. Bring the reinforcing soil almost to the top rim of the band-form.