Flat roof / floor recommendations required

[higgs]

Which waterproofing system would be best for a terrace floor above two bedrooms. The terrace floor is chipboard I believe sitting across the underlying beams. There is a drain to the centre of the terrace so any system needs to be sloped to the centre. There will be people walking around on this terrace so the system needs to be flexible and strong and withstand a few knocks. Currently the floor is a failing fibreglass floor. It would be great if I could get some decent advice on this as I've been ripped off a couple of times now for a liquid rubber roof and a fibreglass roof. Both of which have failed. If there is a DIY solution then I will consider that too as it's broken the bank and the cowboys are not refunding the money. Thanks for any advice and replies. Also is there anything I can do to recover my money or is it not worth pursuing?

[Mr Punter]

Where is the insulation?  I suspect you may need to strip the lot and start again.  I am not a fan of the central drain.  Unless you get this properly designed you will be messing about forever.

[higgs]

The insulation is between the terrace chipboard floor and the wooden/steel beams under the terrace floor. Also these beams etc lie above the two bedrooms in the ceiling. Yes I don't like the central drain either. Weirdly the neighbour has the same design and seemingly no leaks. So it seems it comes down to choice of water proofing for the terrace. I can't tell what he has used as it's covered up with artificial grass on the terrace. I think I'll ask him also if they have had any issues. 

[Conor]

Is there flashing around chased in to the wall? The fibreglass does look really poor and I can see the joints between the boards underneath. These should be filled and double taped to prevent cracking. If your timber structure and deck aren't up to spec, then any roof system could fail.