On mine the hole was dug and then the steel was put in place suspended from two very large wooden beams. Boxing was also put round the hole to allow the foundation to be higher than the ground. So all the reinforcements and the long bolts and base plates where assembled and level before the concrete was poured.
The concrete then arrived and was laid and vibrated into the hole and allowed to come up to level with the top of the base plate. It was then finished off, cleaned skimmed etc.
I have pics of the whole process and will post them, but I find it such a pain resizing them.
Hope this helps?