You do normally produce concrete blocks locally; they have a relatively low value but weigh a lot so it is not cost efficient to carry them very far. If you are going to do a lot and are not too concerned about quality or finish (as here) you can even produce them on site. Only about 10% is actual cement (the very alkaline powder from the cement factory), the rest is water, stone (aggregate) and sand, which is all local supply. They also weigh about 2 tons or more per cubic yard so are difficult to handle without a crane, as anyone who has put even paving slabs down in their back garden can testify !
Depending on the weight to be supported you may need to have reinforcing steel rods inside, but maybe they got away without that for fighters. In fact the bowser probably had a greater surface loading than the aircraft.
You can see by the grass gaps in 2 dimensions between them that drainage was simply a matter of letting rainwater percolate down the cracks between the blocks into the soil; I can't see if there were additional drainage holes in the blocks. Drainage is the main problem in a proper concrete hardstanding or runway, putting it in costs much more than the cost of the concrete structure, and getting the slope right so the rainwater runs the right way is another issue. However this example here is simplistic stuff and they were doubtless not too bothered at the time about the finer details.