"CWatters" wrote in message
...
Someone told me that the base should be slightly smaller than the shed so
that rain water runs down the walls and then down the sides of the slab.
If
the slab is bigger then the water can sit on small bit of the slab around
the edge and rot the bottom of the shed. I've no idea if this is a real
problem ot not but it seems to make sense. The problem with making it
smaller is the accuracy required.

It is a real problem, but more to bounce than to sitting in puddles

Water hits concrete base, bounces up and then rots the
floor from below.

Remedy is a rubber skirt (strips cut from excess pond liner)

and then also a gutter on the side of the roof (feeds a water butt)


Not a problem for the bounce up to the side of the shed
because that's usually treated.