Blairadamwitch wrote:

Do they come with a floor or do you have to create a concrete or paved
base for them to sit on?

The normal metal sheds don't come with a floor, although kits may be
available separately. I put mine on an existing slabbed patio-type
arrangement. It is very important that the base be flat - if not you
will find parts of the shed not lining up as you try to assemble it.

How are they attached to the ground

Mine had a horizontal plate with a hole in it at each corner, and large
(10mm diameter?) screws and rawl-plugs to bolt it into the base. I think
it may even have included the necessary drill bit, though I used my own
much better one. Of course, this will only work if your base itself is
solid and unlikely to part company with the ground :-)

Pete