Just acquired a neighbouring garage (rental) - typical '60s sectional
concrete stuff, and of course the local y00f have been having a go at
the asbestos cement board roof.

Any advice on fixing / strengthening such a thing? It's a low-crime
area (small village) rather than downtown Bristol any more, but it
still needs all the help it can get.

In particular, where's a good mail-order for things like J-bolts, the
hook-shaped bolts that are common for holding down garage roof boards,
but not quite common enough for Screwfix or Toolstation? Are
http://www.fwb.co.uk any good?

Thanks