On 28 Mar, 16:29, JimK wrote:
pondering a green roof for me garage/store extravaganza....

Information sources are hard to find. There are some nice books out
there at the architectural scale, but little about constructional
details for DIY. However the big-scale books can be useful for
justifying the roof at all (Look dear, It's not just hippies, look
real architects are doing them!) and the plant guidance is useful.
Planting Green Roofs and Living Walls
Nigel Dunnett and Noёl Kingsbury
http://www.amazon.co.uk/exec/obidos/ASIN/0881929115/codesmiths

Most UK-based information of small-scale projects seems to come from
Sheffield Uni. CAT at Macynlleth were depressingly clueless.

The Living Roofs website has a downloadable PDF for a tenner(ish) that
is worth getting, as it's dealing with the sort of project scale we're
interested in. Free sample pages too.
http://www.livingroofs.org/diy-guide-green-roofs.html
Be warned, I had a lot of email trouble dealing with them and actually
getting hold of my copy. Nice people, but it was an uphill struggle
and their webbery isn't working right.

There's a lot of commercial project information out there too, from
people like Oldroyd who make sophisticated membranes
http://www.safeguardeurope.com/products/oldroyd-green-range.php
Don't let the pricetag put you off immediately. This stuff has major
advantages for convenience and speed of working. You can do better
with zero-charged DIY, but if you're building a lightweight (i.e. thin
layer) roof with employed labour, these membranes would have a lot
going for them, especially for steeper pitches.

You need some careful design, i.e. spreadsheets. Estimate your
thicknesses, your weights, and your materials costs - including
planting costs. There are several ways to build a roof and they do
vary by cost / workload / pitch angle / weight / soil demand / plant
compatibility. Your choice, but understand what these compromises are
before starting and choose something that suits your needs, budget,
looks and plants before starting to build it.