Hi Charles,
Whilst I broadly agree with your comments on concrete all of the Greenhouses I have come across have a totally or partial solid floor. The older ones are usually covered with flagstones (these are Victorian Greenhouses) whilst more modern houses use primarily concrete. Some I have seen have wooden flooring.
There are many advantages to covering the bare soil in this way most notably the ease of keeping the area clean, heat retention during the night and the cooling effect during daytime.
As I said putting a beautiful greenhouse structure on top of bare soil is akin to building a very expensive giant cloche and you would, it would, be less expensive and more practical to construct a Polytunnel instead.
I view the greenhouse as the garden workshop, used for raising healthy seedlings, cuttings and protecting vulnerable plants during winter. And of course it could also be used for growing certain tender crops as you would in the polytunnel.
Don.
