Now the mistakes:

* OSB should be OSB3 (quality grade) to qualify for category 2 (usage
grade), such as roofing. I shopped local, wanting to support the
local merchant, and was instead sold OSB2 for use in roofing - it's
not up to it. My attempted remediation was to apply the bitumen paint.

* I've a (doubled) polyethylene DPM on top of polystyrene foam, rather
than a geotextile interleaf (as I used over the timber). Maybe this
will be a future issue with plasticiser leachout, as for PVC cables?

* The Verspanel fascia boards are purely decorative, but still too
thin. This stuff is always brittle - 6mm is unusable without extreme
care, 10mm is dodgy for anything outdoors. Livingroofs use 3/4" thick!

* October isn't a good time to build one, unless you have time
available to build it all in one blast. Otherwise you're off into
November, which then really isn't a good time to be doing it. My
combination of November worktimes being limited to weekends, and
unpredictable weather that I had to just work through anyway, meant
that I was laying liners in a gale. Although this was an excuse to
wear my copper hat and shout "All Gods are *******s!" while standing
on a roof in a thunderstorm.

* I ordered Perlite, but was delivered Vermiculite. There's not much
between them, but Perlite grains are less crumbly and a lot less wind-
blown. See above about working in storms.

* The fall (1 brick in 8') was insufficent, and I think the soil is
going to remain too damp over Winter. Should have used a whole block
height instead.

* My outfall pipe outlet through the liner is a bit of a hack and I
should have been more careful with it. Bitumen mastic hides a great
many sins.

* The outfall pipe was initially too high, so I dropped it by half an
inch later on. In combination with the shallow pitch, it just can't
drain the roof adequately and it leaves too much standing water behind
afterwards. I should probably have sunk it locally into the
insulation, to get another 1/2" below the majority of the liner.