"Mr Green" wrote in message
...
I am reseating a greenhouse on a concrete base - about 8ft x 6ft.

I will seat it on tanilized timber lats of say half inch x one and a
half inches - with rawl-bolts in the base - through the lats - and
then through the green-house base.

The base is not perfectly level - once side appears to be about half
an inch on the low side wrt the other three sides


I would organise it so that the point you want the rain to run off into your
water butt(s) is the lowest. Most people sit the greenhouse on its base then
see where the water comes off and put the butts that end, which is a bit of
a bugger if it's the inconvenient end.

Steve