first how large is the planned shed?
the work to mix and place concrete is a LOT
if you need just a small amount bags are great, but get a larger shed
and the bags costs will kill you.
so please tell us more about your plans!
In general a bigger shed is always best, since i will fill up fast:(
A good experiment take EVERYTHING your planning on putting in shed
together, then put it all in a similiar space like part of garage,
leave room for door!
around here even larger sheds can be built on a floating slab with no
footer needed, my 16 by 20 has no footer.
some people build wood sheds with treated wood floors, not for me but
worth checking out.
In addition there are shed companies that build nice affordable sheds
in a day. In the fall they sometimes run sales....
Many cut and build assemblies in their shop and just assemble the
pieces in your yard. Done with jigging and made to be moved they tend
to be very strong.
Go BIG or you will rember my warnings when your shed is JAMMED:(
GEEZ I SHPOULD OF LISTENED:(:(