DIYbanter - Flat roof repair

I had one done a couple of months ago, to a two-storey, 2m x 2m area
extension. The old flat roof was leaking and needed replacing, including
all the timber decking which was by this time rotten (bit of a mess really).
Job was done and paid for and looked like a nice job when I went up my
ladder for a quick shufti.

However, recently I had the ladders out again to sort out a guttering
problem(*). This was about one day after a hefty downpour. I discovered
that most of the new flat roof was about 1" deep in rainwater, simply
because it slopes back towards the house rather than towards the (apparently
totally redundant) gutter along the front of the roof.

Having all that water floating about up there is clearly bad practice, but
do I have a grouse against the roofer about it? He's probably just replaced
like with like and replicated the problem of a poorly built roof (I'm
guessing the original was bad, which would account for the extent of the
leaking problem), but as part of reinstating my roof, wouldn't it have been
a fairly trivial matter to correct the slope, and shouldn't he have at least
mentioned this to me while doing the job?)

The roofer is one who I trust (I once had him in to quote for what I thought
was a full re-roofing job, and he charged me about 50 quid for a few new
tiles which was all that proved necessary), and who - normally - does a very
good job, so I don't want to tackle him about this issue if I'm being
unreasonable.

Thanks
David

(*) An aside - I was bemused and I suppose slightly irritated by all the
drivers slowing down and gawping up at me from their cars as they approached
the junction (I'm on a corner). Suddenly BAM!! one of them rear-ended the
bloke in front. Ha! Although they subsequently both kept looking up at me
while exchanging insurance details, at least nobody tried to point the
finger of blame in my direction. But I wonder if I feature in the claim
forms?!