shazzbat wrote:

I was thinking of the ones I knew in Manchester when I was a kid. Brick
built with an enormous concrete slab for a roof. We had had one in our
garden, but it was reduced to ground level and turned into a pond by the
time I was born (baby boomer)

I have seen one like that in a Stoke-on-Trent garden.
The thick concrete slab was made with zillions of surplus clay pipes
(the smoking variety).
Not enough tobacco to go round in them days? ;-)

Jiri Borsky