The design requirement for a man load on flat roof joists will mean it
can carry almost as many growbags as you require.

Loading is almost certainly not a factor in this case. If you want me to
check then get the size of the flat roof joist, with the longest
distance between supports and I`ll do a quick calc to prove the loading
for you. 8-)

--
email farmer chris on
Please don`t use as it`s a spam haven.