Hi Freed,
I’m sure Charles will give you his own take on this but if I might offer my own opinion.
I see Greenhouses and Polytunnels thus.
A Polytunnel is nothing more than a giant cloche where as a Greenhouse is the Garden Workshop used primarily for raising seedlings and housing tender plants over winter.
Of course you can grow crops such as Tomatoes etc in the Greenhouse but you don’t have to plant into bare soil to do so.
If I had a Greenhouse I would definitely want a concrete floor. Constructing a Greenhouse on bare soil seems to me to be a very very expensive cloche.
Don.