I have paving slabs down the middle and soil, either side for growing toms/peppers etc in.
You may prefer to have it all slabs or even concrete. depends on what you want to do with it. dont forget to set the frame on a solid 'base', mine is concrete, though my father in law had his on tanalised timber.

It all depends on what you want to use the greenhouse for,some people use paving slabs to cover the floor area as they only use theirs for new seedlings to give them a head start in life,and others use concrete blocks with a path down the middle to leave a bed each side for planting,Remember what ever you use it has to be secured with rawl plugs and screws,good luck and welcome to g.o.y.

As above, it depends what you want to use it for. Ours is paved down the middle and on the north side (for staging to stand on) and I have a raised plunge bed on the south side. I wouldn't recomend as concrete floor as you are then stuck with it. Paving slabs can be removed at a later date if you change you mind.

One of the most important things is to make sure that the part that the sides and ends stand on is firm, not just on soil. Otherwise the glass will break or come loose. Mine has a concrete 'bar' all around the edge and the g'house is screwed into that.
Soil in a g'h needs replacing regularly if used to plant into, so bear that in mind.

yes mine is on a 'band' of concrete. I have to replace the soil this year too :o(
it is a job I really hate.

thnx 8)