I'm repairing a flat concrete roof which has spalled a bit in one corner
(posted about this a few weeks back actually); could I have some
recomendations for how to finish off the top surface afterwards? The
whole area is about 10m2; it was previously covered with the crabby
remnants of some form of bitumen-based stuff which I've just blasted off
with some help from my mate Karcher.

Screwfix seem to have a huge variety of different roofing chemicals, and
I haven't a clue which to go for.
http://www.screwfix.com/app/sfd/cat/...02009&ts=71109
I'm thinking this one?
http://www.screwfix.com/app/sfd/cat/...71119&id=69277

How long do I let the cement dry in the repaired area (about 1m2, up to
about 3" deep) before applying it (the underside of the roof is open to
the air)

Thanks for any advice
David