You may well find that B&Q will be amongst the cheapest, however, you
will be better going to a local shed and garage retailer who will
supply you with a shed made of a sturdier thickness of panelling. Our
local supplier here in York, Garasheds, is also a keen gardener and
allotment holder and grows and sells a wide variety of plants at
bargain prices on his site as well as selling the sheds, garages and
greenhouses that are his main trade. That reminds me, as it is near the
end of the season he might have a few fuchsias to sell off cheap so I
must pay him a visit in the next day or two.